Abstract
Lineage plasticity and histologic transformation to small cell neuroendocrine prostate cancer (NEPC) is an increasingly recognized mechanism of treatment resistance in advanced prostate cancer. This is associated with aggressive clinical features and poor prognosis. Recent work has identified genomic, epigenomic, and transcriptome changes that distinguish NEPC from prostate adenocarcinoma, pointing to new mechanisms and therapeutic targets. Treatment-related NEPC arises clonally from prostate adenocarcinoma during the course of disease progression, retaining early genomic events and acquiring new molecular features that lead to tumor proliferation independent of androgen receptor activity, and ultimately demonstrating a lineage switch from a luminal prostate cancer phenotype to a small cell neuroendocrine carcinoma. Identifying the subset of prostate tumors most vulnerable to lineage plasticity and developing strategies for earlier detection and intervention for patients with NEPC may ultimately improve prognosis. Clinical trials focused on drug targeting of the lineage plasticity process and/or NEPC will require careful patient selection. Here, we review emerging targets and discuss biomarker considerations that may be informative for the design of future clinical studies.
Introduction
The treatment landscape of advanced prostate cancer continues to evolve. Drugs with varied mechanisms of action now being used in earlier disease settings, and patients are living longer with longer exposure to systemic therapies. However, systemic therapies are not curative, and the treatment-resistant state remains a major medical problem. Resistance mechanisms in prostate cancer are diverse, dependent on the biologic pathways targeted and typically occur in the context of activated androgen receptor (AR)-signaling. While the AR is the main key driver of prostate cancer initiation and progression, a subset of prostate cancers either start relatively AR-independent or, more commonly, they acquire AR-independence during the course of their disease. The frequency of AR-independence has been reported in up to 15–20% of CRPC tumors after treatment with potent AR-targeted drugs (e.g. abiraterone, enzalutamide) (Bluemn et al. 2017, Aggarwal et al. 2018, Abida et al. 2019). Developing effective therapies for AR-independent prostate cancer is particularly challenging, as there is heterogeneity even within this subset and continued clonal and sub-clonal evolution of castration-resistant tumors as they progress. One increasingly recognized mechanism of AR independence is lineage plasticity, a process that involves the acquisition of alternative lineage programs to drive cancer growth and progression (Beltran et al. 2019) (Fig. 1). These alternative programs, commonly of neuronal or neuroendocrine lineage, are pointing to acquired pathways and targets that may be exploited therapeutically. Clinically, lineage plasticity may manifest as a histologic transformation from a prostate adenocarcinoma to a small cell neuroendocrine carcinoma (Beltran et al. 2011, Bluemn et al. 2017, Aggarwal et al. 2018). As new drugs enter the clinic for neuroendocrine prostate cancer, patient selection will be critical.
Schematic of the lineage plasticity process in prostate cancer.
Citation: Endocrine-Related Cancer 28, 8; 10.1530/ERC-21-0140
Missing link: why we need biomarkers
With increased recognition of diverse castration-resistant prostate cancer (CRPC) subtypes, metastatic biopsies are increasingly being performed. Genomic sequencing to look for actionable targets (e.g. DNA repair alterations) is now considered a standard of care. Metastatic biopsies have also identified morphologic heterogeneity within and across patients with CRPC. While most CRPC tumors retain characteristics of prostate adenocarcinoma, some may become poorly differentiated losing their luminal structure and/or acquiring characteristics of classical small cell carcinoma (Epstein et al. 2014). Small cell carcinoma is considered a poorly differentiated neuroendocrine carcinoma and can look and act similar to small cell neuroendocrine carcinomas arising in other anatomic sites (e.g. small cell lung cancer (SCLC)). While immunohistochemistry (IHC) is not required for the diagnosis of NEPC, IHC is often performed clinically as cells typically express classical neuroendocrine markers such as chromogranin, synaptophysin, INSM1, NSE, CD56 (Epstein et al. 2014). It is important to note that expression of these neuroendocrine markers is sometimes observed in poorly differentiated/high-grade adenocarcinomas. Large cell carcinoma variants or tumors with mixed features of small cell or large cell carcinoma admixed with classical prostate adenocarcinoma are also observed in later stages of prostate cancer. The term ‘neuroendocrine prostate cancer (NEPC)’ has been used to broadly encompass prostate cancers that have neuroendocrine features based on morphology and IHC staining for neuroendocrine markers. While NEPC tumors often lack expression of the androgen receptor (AR) and downstream AR-regulated targets (such as prostate-specific antigen (PSA)), this is not universal, reflecting the spectrum and continuum of lineage plasticity (Beltran et al. 2019). Of note, a subset of CRPC tumors lack morphologic features and IHC markers of NEPC and also lack AR expression and have thus been termed ‘double negative prostate cancer’ (Bluemn et al. 2017). Whether this represents a distinct entity or a state within the continuum of lineage plasticity toward NEPC is not well established clinically. Other acquired alternative lineage phenotypes such as squamous and gastrointestinal programs have also been observed in later stage CRPC (Shukla et al. 2017, Labrecque et al. 2021), suggesting potentially differential trajectories within the lineage plasticity process. Clinically, patients with NEPC typically develop progression in the setting of low or non-rising serum PSA levels (but not always) and may have elevated serum neuroendocrine markers (such as chromogranin, NSE) or carcinoembryonic antigen (CEA) levels and/or develop visceral or atypical sites of metastases (e.g. lytic bone, parenchymal brain) (Conteduca et al. 2019). While these clinical characteristics are not specific for NEPC, aggressive clinical features have been used as inclusion criteria for clinical trial enrolment (Aparicio et al. 2013, Corn et al. 2019). Specifically, the aggressive variant prostate cancer (AVPC) criteria have been used within platinum chemotherapy trials in CRPC and include the presence of exclusive visceral metastases, low PSA and bulky disease, high lactose dehydrogenase levels, elevated CEA, lytic bone metastases, and/or NEPC histology (Aparicio et al. 2013).
While most NEPC tumors are recognized in later stages after patients have had prior therapies for metastatic CRPC, they can also arise de novo, either as pure small cell carcinoma or mixed with high-grade adenocarcinoma. Both treatment-emergent and ‘de novo’ NEPC share common genomic aberrations as prostate adenocarcinoma (e.g. with the prostate cancer-specific TMPRSS2-ERG fusion present in approximately 40–50%) (Beltran et al. 2011, Chedgy et al. 2018), supporting their common cellular origin, but they are enriched with certain acquired alterations including loss of RB1 and TP53–alterations universally present in other poorly differentiated neuroendocrine carcinomas such as SCLC and acquired in EGFR-mutated lung adenocarcinomas that transform to SCLC (George et al. 2015, Niederst et al. 2015, Beltran et al. 2016b, Park et al. 2018). The presence of RB1 loss or combined tumor suppressor losses (RB1, TP53, PTEN) in men with CRPC even without histologic evidence of NEPC has been associated with aggressive disease and poor prognosis (Aparicio et al. 2016, Abida et al. 2019). Epigenetic alterations, including changes in DNA methylation, chromatin accessibility, SWI/SNF, and histone marks are distinguishing features of NEPC, suggesting a key role of epigenetics in driving histologic transformation (or trans-differentiation) from prostate adenocarcinoma to NEPC (Beltran et al. 2016b, Dardenne et al. 2016, Cyrta et al. 2020, Baca et al. 2021). Activation and coordination of lineage determining transcription factors (e.g. ASCL1, BRN2, ONECUT2, MYCN, FOXA1) (Dardenne et al. 2016, Lee et al. 2016, Bishop et al. 2017, Rotinen et al. 2018, Guo et al. 2019, Baca et al. 2021), pluripotency factors (e.g. SOX2) (Bishop et al. 2017, Mu et al. 2017), and homeobox genes (eg. HOXB5, HOXB6) (He et al. 2021), as well as dysregulation of prostate cancer genes in the context of AR therapy (eg. ERG, SPINK1) (Mounir et al. 2015, Tiwari et al. 2020), and/or downregulation of other transcription factors (e.g. REST) (Lapuk et al. 2012, Zhang et al. 2015) further drive transcriptional changes and associated lineage reprogramming (He et al. 2021). This lineage reprogramming may be mediated by an intermediary, de-differentiated ‘stem like’ state before cells differentiate toward a neuronal developmental/neuroendocrine-like phenotype with loss of AR dependence (Fig. 1). Based on the study of metastatic tumors, we developed a 70-gene signature (NEPC score) that distinguishes NEPC from prostate adenocarcinoma (Beltran et al. 2016b). Interestingly, this NEPC score has been found to be inversely correlated with AR signaling not only in metastatic CRPC (Abida et al. 2019) but also in primary untreated tumors (Mahal et al. 2018).
With significant advances in our understanding of the biological underpinnings of lineage plasticity and the mechanisms that drive the development of NEPC, there is a growing need for biomarkers to (1) more accurately diagnose NEPC in the clinic and (2) potentially predict NEPC transformation before it develops or identifies patients in the process of lineage plasticity while progressing on standard therapies for early intervention strategies. This has important therapeutic implications. For instance, if the target of interest is expressed only when neuroendocrine lineage is present, then an accurate biomarker to identify NEPC and/or the target would be needed. If the goal of therapy is to prevent or reverse lineage plasticity (for instance, through epigenetic modulation), then a biomarker to identify tumors without neuroendocrine differentiation would be ideal, and co-targeting or alternating strategies (targeting AR and non-AR pathways) may be rationally developed.
Relationship between target and therapy
Patients with histologically confirmed small cell NEPC or CRPC with aggressive variant clinical features (AVPC) are often treated with systemic therapy regimens used for SCLC, based on clinical, pathologic, and molecular similarities between NEPC and SCLC (Berchuck et al. 2021). Similar to SCLC, they tend to be initially responsive to platinum-based chemotherapy with objective response rates of 50–60% (Sella et al. 2000, Papandreou et al. 2002). The combination of carboplatin with the taxane chemotherapy cabazitaxel is now supported by the National Comprehensive Cancer Network (NCCN) guidelines as an option for patients with aggressive variant clinical features or unfavorable genomics (loss of function alterations involving at least two of PTEN, TP53, and RB1). In a phase II study, 113 men meeting AVPC clinical criteria were treated with carboplatin plus docetaxel followed by cisplatin plus etoposide at progression (Aparicio et al. 2013). The median progression-free survival (PFS) with carboplatin plus docetaxel was 5.1 months, and the median overall survival was 16.0 months (95% CI 13.6–19.0) (Aparicio et al. 2013). In a follow-up randomized phase II study (Corn et al. 2019), 160 men with metastatic CRPC, stratified by the presence of AVPC features, were randomized to cabazitaxel vs cabazitaxel plus carboplatin. There was a more substantial improvement in PFS favoring combination chemotherapy (cabazitaxel plus carboplatin) in men with AVPC (HR 0.58 (95% CI 0.37–0.89) compared with those without AVPC (HR 0.74 (95% CI 0.46–1.21)). The mechanisms of response of NEPC and AVPC to this regimen may also be influenced by underlying tumor suppressor loss and/or DNA repair aberrations. The combination of cabazitaxel with carboplatin has a particular rationale in NEPC, given the activity of cabazitaxel in CRPC and mixed tumor histologies (both adenocarcinoma and NEPC elements) frequently observed within the spectrum of NEPC (Epstein et al. 2014).
For those patients with pure small cell carcinoma, SCLC regimens such as carboplatin-etoposide with or without the anti-PDL1 immune checkpoint inhibitor atezolizumab (based on the IMpower133 trial (Horn et al. 2018)) may also be considered. Docetaxel with carboplatin is also a reasonable option for patients who have not previously received docetaxel, given the frequent mixed CRPC/NEPC features. A major clinical challenge is in what to do next after platinum-based chemotherapy. There are limited data in the second line and beyond settings. For mixed tumors with both adenocarcinoma and NEPC elements, the choice of therapy depends on the dominant histology and clinical context. Next line SCLC regimens may be considered for those with small cell NEPC; these include lurbinectedin, topotecan, pembrolizumab, ipilimumab/nivolumab. Given limited data, we would encourage participation in clinical trials. Further, ADT should be considered in both de novo and treatment-related NEPC cases (even small cell carcinomas) given tumor heterogeneity.
Emerging targets for lineage plasticity and NEPC have been discovered through combined clinical and preclinical studies (Fig. 2), and several trials are now underway. Several of these targets are shared with SCLC, such as DLL3, AURKA, EZH2, and DNA repair pathways. Understanding the relationship between target expression and pathway activation with therapeutic responses to these agents will be critical for patient selection, especially since these features may not be present at the time of the patient’s initial diagnosis. NEPC tumors express cell surface markers that may be exploited therapeutically. CEACAM5 (carcinoembryonic antigen-related cell adhesion molecule 5) and DLL3 (delta-like ligand 3) are two examples of cell surface proteins also present in other cancers such as colon cancer and SCLC, respectively (Thompson et al. 1991, Saunders et al. 2015). Lee et al. (2018) evaluated cell surface profiles using gene expression data and validated CEACAM5 as a marker enriched in NEPC and a promising target for cell-based immunotherapy. As a proof of concept, they developed an engineered chimeric antigen receptor T cells targeting CEACAM5, which induced antigen-specific cytotoxicity in NEPC models (Lee et al. 2018). Further clinical investigation targeting CEACAM5 is planned for men with NEPC. We identified DLL3 as another cell surface protein, a notch inhibitory ligand, highly expressed in the majority of NEPC (76.6%) as well as a subset of aggressive CRPC tumors (12.5%), and not expressed in benign tissues (Puca et al. 2019). DLL3 is being investigated as a therapeutic target for both NEPC and SCLC. The anti-DLL3 × CD3 Bi-specific T cell Engager AMG757 (Amgen) and the DLL3-targeted tri-specific T cell activating construct HPN328 (Harpoon) are in early phase clinical trials (NCT04471727, NCT04702737).
Representation of relative abundance of features and patient-based studies and models along the continuum from localized prostate cancer (PCa) to castration-resistant adenocarcinoma (CRPC-Adeno) to androgen receptor (AR)-independent CRPC. The schematic includes the frequencies of relevant genomic and epigenomic aberrations associated with neuroendocrine prostate cancer and the relative number of patient-based studies and models that exist to study each of these disease states, evidencing the yet modest availability of tissue-based and liquid biopsy-based studies in the setting of AR independent CRPC, where disease control is especially limited. AR, androgen receptor; CRPC, castration-resistant prostate cancer.
Citation: Endocrine-Related Cancer 28, 8; 10.1530/ERC-21-0140
Other immune targeted approaches are also being investigated in NEPC. Though immune checkpoint inhibitors are commonly used in SCLC and sometimes extrapolated to treat small cell NEPC, there have been limited data reported to date for this subgroup of prostate cancers. In a recent study by Brady et al. (2021), digital spatial profiling revealed that the majority of metastatic CRPC and NEPC tumors are devoid of significant inflammatory infiltrates and lack PD1, PD-L1, and CTLA4. Consistent with this, Brown et al. (GU ASCO 2021) recently reported results of 19 patients with NEPC or aggressive variant clinical features treated with the PD-L1 inhibitor avelumab in a single-arm phase 2 study (NCT03179410). Radiographic response rate was 6.7%. One complete response was observed in a patient that also harbored tumor microsatellite instability and MSH2 mutation. Median radiographic progression-free survival was 1.8 months (95% CI 1.6–2.0) and median time on therapy was 56 days (range 28–356). Median overall survival was 7.4 months (85% CI 2.8–12.5). Given this limited single-agent activity, combination immunotherapy is now being tested. Ongoing clinical trials include a phase 2 basket study of ipilimumab plus nivolumab for rare GU tumors with a small cell carcinoma arm (NCT03333616), a phase 1/2 study of pembrolizumab plus BXCL701, an oral innate immunity activator (NCT03910660), and a phase 1 study of pembrolizumab in combination with platinum-based chemotherapy (NCT03582475).
NEPC tumors express higher levels of cell cycle genes including aurora kinase A (AURKA), aurora kinase B (AURKB), and polo kinase (PLK1) (Beltran et al. 2011). Aurora-A has also been shown to stabilize N-myc during NEPC progression (as also observed in neuroblastoma, another neuroendocrine tumor (Otto et al. 2009)). Expression of Aurora A has also been linked mechanistically with TP53 mutation via expression of miR-25 leading to reduced levels of FBXW7 which encodes an E3 ubiquitin ligase that regulates Aurora A (Li et al. 2015). Targeting aurora kinase in the context of underlying RB1 loss (present in the majority of NEPC) is synthetically lethal (Gong et al. 2019, Oser et al. 2019), providing additional rationale. The Aurora kinase A inhibitor alisertib was tested in a phase 2 clinical trial for patients with clinical or pathologic features of NEPC (Beltran et al. 2018). Though this study did not meet its primary endpoint of PFS in a biomarker-unselected population, exceptional responders were observed. Further investigation, potentially in the context of N-myc gain or RB1 loss, may be warranted. Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase that also cooperates with N-myc to drive neuroendocrine differentiation, and chemical and pharmacologic inhibition of ALK has shown activity in preclinical models of both NEPC and N-myc-driven neuroblastoma; these data point to additional potential shared vulnerabilities between NEPC and other neuroendocrine tumors that may be exploited clinically (Unno et al. 2021). RET is another kinase identified as preferentially activated in NEPC with potential therapeutic implications (Drake et al. 2013). Although the phase 3 trial of cabozantinib (which targets RET as well as other kinases such as MET, VEGFR2, FLT3, c-KIT) was negative for overall survival in metastatic CRPC (Smith et al. 2016), it is currently being evaluated in a biomarker-selected subgroup of CRPC (NCT04631744) as well as in combination with atezolizumab (NCT04446117).
Targeting DNA repair is an area of interest in NEPC, given clinical responses to platinum chemotherapy and similarities with SCLC. The frequency of genomic aberrations involving DNA repair pathways is similar in treatment-related NEPC as other CPRC tumors (approximately 20% harboring pathogenic mutations in homologous recombination genes), and potentially more common in de novo cases (Beltran et al. 2016b, Chedgy et al. 2018). Upregulation of DNA repair genes in NEPC has also been associated with activation of PARP1/2 by N-Myc (Zhang et al. 2018, Liu et al. 2019). While poly (ADP-ribose) polymerase (PARP) inhibitors are currently indicated for specific genomic alterations linking with the Food and Drug Administration (FDA) label in CRPC, their use in additional contexts is not yet established. A phase 2 study of induction chemotherapy with carboplatin plus cabazitaxel followed by maintenance PARP inhibitor therapy with olaparib in patients with aggressive variant clinical features including NEPC is ongoing (NCT03263650). The combination of PARP inhibitor and ataxia telangiectasia and rad3-related (ATR) inhibitor therapy has also shown preclinical activity in CRPC tumors with combined TP53 and RB1 loss, reflecting a potential targetable vulnerability resulting from replication stress (Nyquist et al. 2020). In SCLC, combined inhibition of ATR (bertosertib) and topoisomerase (topotecan) is also synergistic; an overall response rate of 36% was seen with this combination including durable regressions in patients with platinum-resistant disease (Thomas et al. 2021). SCLC tumors with high neuroendocrine differentiation and enhanced replication stress were more likely to respond. These data suggest that replication stress may also be a potential therapeutic vulnerability in NEPC.
Though lineage plasticity may be facilitated by underlying genomic aberrations, such as loss of RB1 and TP53, the most striking differences between NEPC and prostate adenocarcinoma are epigenetic. Recent DNA methylation, ChIPseq, and ATACseq studies support transcriptional reprogramming mediated by epigenetic regulators and driven by key lineage determining transcription factors (TFs). EZH2 is an epigenetic regulator, part of the polycomb repressive complex 2 (PRC2), involved in histone methylation (H3K27me3) and gene repression. EZH2 is overexpressed in CRPC compared with primary tumors, and even more so in NEPC (Beltran et al. 2016b, Ku et al. 2017, Puca et al. 2018). There is a suggestion based on preclinical studies that targeting EZH2 can reverse plasticity in the setting of underlying tumor suppressor loss or N-myc gain, re-sensitizing tumors to enzalutamide (Dardenne et al. 2016, Kleb et al. 2016, Ku et al. 2017). EZH2 can also activate the AR in the setting of AR-driven disease (Xu et al. 2012). Clinical trials investigating the combination of EZH2 inhibitor therapy with potent AR inhibition are underway for late-stage CRPC (NCT03480646, NCT03460977, NCT04179864). Ongoing correlative studies may elucidate molecular subsets within responders in these trials.
Targeting other epigenetic regulators, such as LSD1, BET, or DNA methyltransferase, are also under investigation in advanced CRPC and may have a rationale in NEPC (Conteduca 2021). Current ongoing trials of epigenetic drugs are also without patient selection for NEPC. Similarly, correlative studies may elucidate molecular mechanisms of response in these trials. This will require not only studying mediators of anti-tumor activity but also potential changes in tumor lineage programs that occur on therapy. DNA methylation changes, in particular, are distinguishing features of NEPC, detectable in both metastatic tumors and cell-free DNA (plasma) of patients (Beltran et al. 2016a, 2020, Zhao et al. 2020). Integration of DNA methylation with transcriptomic data suggests epigenetic regulation of cell–cell adhesion, developmental, and stem-like pathways. Targeting DNA methyltransferases and/or other upstream mediators that regulate these processes are approaches under investigation. Of note, downregulation of protein kinase C (PKC) λ/ι results in the upregulation of serine biosynthesis and increases intracellular S-adenosyl methionine levels in NEPC, pointing to a potential metabolic regulation of DNA methylation during lineage plasticity (Reina-Campos et al. 2019). Additionally, the downstream TFs that mediate transcriptional changes associated with lineage reprogramming, such as BRN2, ASCL1, FOXA1, ONECUT2, MYCN, and others may also serve as potential therapeutic targets though TFs are much more challenging to target directly. Understanding the mechanisms and timing of epigenetic events and their cooperation in promoting and/or sustaining plasticity will be important for the development of rational biomarkers and combination strategies. If AR can indeed be re-activated by targeting epigenetic alterations, then combination or bipolar/alternating strategies may be tested.
Emerging biomarkers
Several tissue-based studies and preclinical studies have identified genomic, transcriptomic, and epigenetic differences between castration-resistant prostate adenocarcinoma and NEPC (Beltran et al. 2019). While these studies have fueled mechanistic studies and validation of new targets, in practice obtaining metastatic biopsies for extensive molecular analyses is a major clinical challenge. Biopsies, when performed to evaluate for NEPC, are often small and prioritized clinically to confirm the diagnosis (tumor morphology, IHC) and for targeted genomic assays to identify targets for FDA-approved therapies (e.g. olaparib, rucaparib, pembrolizumab). IHC staining for classical neuroendocrine markers is commonly performed clinically and may potentially be improved upon with other NEPC-associated markers that can be measured in situ (e.g. IHC for RB1, DLL3, ASCL1, SWI/SNF complex members). The presence of combined tumor suppressor loss (RB1, TP53, PTEN) is often detected on targeted genomic assays in patients with NEPC as well as those with aggressive variant clinical features and may help identify patients for more aggressive systemic therapy regimens such as platinum-based chemotherapy, as recently endorsed by the NCCN (Aparicio et al. 2016). The timing of their acquisition and evolution of these tumor suppressor losses, and the contribution of other co-occurring genomic and epigenomic DNA alterations, have not been extensively studied. To this end, we evaluated molecular changes in CRPC and NEPC in the context of a few specific drug targets (Fig. 3) illustrating how DNA-based changes (e.g. tumor suppressor loss, DNA methylation) might correlate with targets/pathways in CRPC or NEPC that are non-genomic based.
Gene expression of specific targets (EZH2, AURKA, DLL3) in CRPC and NEPC metastatic tissue biopsies, annotated by genomic tumor suppressor loss, NEPC-associated features informed by DNA methylation changes, and AR signaling. Epigenetic and genomic signals might be indicative of non-genomic-based NEPC relevant targets/pathways. EZH2, enhancer of zeste 2; DLL3, delta-like ligand 3; CRPC, castration-resistant prostate cancer; NEPC, neuroendocrine prostate cancer; AR, androgen receptor.
Citation: Endocrine-Related Cancer 28, 8; 10.1530/ERC-21-0140
Despite the increased recognition of patients with CRPC that progress toward NEPC, the total number of profiled patient tumors in the published literature remains low and there are differences in the diagnostic criteria, platforms, and analytics used. One challenge lies in the need for invasive biopsies. Evaluation of primary tumors suggests that most NEPC features (e.g. histology, RB1 loss, DNA methylation changes) are not typically detected early; however, there may be transcriptomic changes associated with AR independence early on (Mahal et al. 2018, Spratt et al. 2019). Whether these transcriptomic changes predict the future development of NEPC and/or therapy response in earlier disease settings (e.g. AR therapy vs chemotherapy) is yet to be reported. Given that most of the targetable alterations identified in NEPC appear to be acquired during therapy resistance, the development of non-invasive biomarkers (e.g. liquid biopsies, molecular imaging) to detect molecular changes associated with NEPC is a promising approach. Serial assessments allow for the charting of tumor dynamics over time and for specifically analyzing treatment-related changes and target expression. Furthermore, single-site metastatic biopsies do not always reflect the pathologic heterogeneity that may be seen within an individual patient; therefore, non-invasive biomarkers have an additional advantage in more accurately reflecting composite tumor burden and molecular intra-patient heterogeneity.
Especially in the setting of heterogeneous diseases such as metastatic prostate cancer, plasma cell-free DNA (cfDNA) studies have provided valuable observations, both at the genomic and epigenomic level. Relevant to the characterization of NEPC, we analyzed biopsy-confirmed castration-resistant adenocarcinoma and NEPC tumors along with matched cfDNA by whole-exome sequencing and whole-genome bisulfite sequencing and found that (1) cell-free DNA genomics recapitulates the relative contribution of key drivers (including loss of TP53, RB1, PTEN, amplification of MYC, MYCN, and AR), (2) serial sampling can track the emergence and clonal dominance of certain sub-clonal alterations, (3) the level of intra-patient genomic heterogeneity is higher in castration-resistant adenocarcinoma compared with NEPC, and (4) DNA methylation of cfDNA resembles tissue-based data and can identify NEPC-specific features (Beltran et al. 2020). Further, through serial sample analyses, we demonstrated that NEPC-associated DNA changes could be detected in the circulation prior to clinical evidence of NEPC. Key to this initial study was the availability of metastatic tissue biopsies that allowed for the assessment of inter and intrapatient similarities on a metastatic site basis and across sites, leading to the observation that NEPC-associated alterations are generally conserved across sites, and, therefore, the data from cfDNA were not driven by the sites of metastases. There are several commercial platforms available for cell-free DNA analysis. While targeted cfDNA platforms are commonly used clinically in metastatic CRPC to evaluate for actionable genomic alterations, cfDNA methylation platforms such as GRAIL and others have mostly been geared toward cancer detection and minimal residual disease monitoring. Additional work is needed to leverage such technologies for the detection of specific cancer resistance phenotypes such as NEPC.
While the cfDNA sequencing is informative of genomic burden, the mutational load, the presence of specific somatic DNA and DNA methylation events, the noninvasive assessment of transcriptional profiles and expression of key targets are more challenging. Ulz and colleagues recently proposed a method for assessing transcription factor activity via cfDNA (Ulz et al. 2019). Specifically, through whole-genome sequencing of cfDNA and nucleosome footprint analysis, they inferred transcription factor accessibility based on DNA fragmentation patterns. The authors showed the ability to distinguish NEPC from prostate adenocarcinoma based on differential accessibility of the binding sites of AR, REST, HOXB13, NKX3-1, and GRHL2. Potentially combining novel approaches with cfDNA methylation, cfDNA ChIPseq, or other technologies will provide a more comprehensive readout of the epigenetic landscape of NEPC with the ability to track dynamic and functional changes while on therapy.
Circulating tumor cells (CTCs) hold promise for not only detecting tumor burden (e.g. quantifying CTC count) but can also test morphologic differences between NEPC and adenocarcinoma tumor cells, and other drug targets and resistance mechanisms through mRNA or protein analyses. Using the Epic CTC platform, we identified low or absent AR expression, low cytokeratin expression, smaller morphology, and cell clusters more frequently in CTCs from men with NEPC compared to those with castration-resistant prostate adenocarcinoma (Beltran et al. 2016a). In another study of patients with AVPC, the presence of copy number alterations involving at least two tumor suppressor genes and genomic instability in DNA derived from single CTCs was associated with poor survival (Malihi et al. 2020). Overall, CTC heterogeneity has been associated with poor prognosis in patients with CRPC treated with AR-targeted therapies (Scher et al. 2017). In the multicenter PROPHECY study, CTCs were evaluated by the Epic platform in 107 men prior to receiving abiraterone or enzalutamide (Brown et al. 2021). Of these, 8.7% had NEPC features defined by cell morphology and size, and their presence along with chromosomal instability in CTCs was associated with poor prognosis. In addition to providing prognostic value, CTCs are also capable of detecting other tumor features such as expression of AR-V7, SLFN11, and DLL3 (Puca et al. 2019, Armstrong et al. 2020, Conteduca et al. 2020, McKay et al. 2021).
Extracellular vesicles (EVs) derived from metastatic tumor cells can also be detected in the circulation in men with CRPC, including those that are CTC-negative, and may carry tumor-associated proteins that can be quantified and tracked serially (Gerdtsson et al. 2021). The role of EVs as biomarkers to detect lineage plasticity is an area of active investigation (Bhagirath et al. 2021). There are also emerging data regarding the ability of EVs to reprogram cells and they may play a functional role in driving lineage plasticity. For instance, EVs from integrin αVβ3 expressing prostate cancer cells are capable of stimulating tumor growth and driving neuroendocrine differentiation in tumor models (Quaglia et al. 2020).
Molecular imaging is another emerging non-invasive biomarker in CRPC. Recent studies have been focused on detecting prostate-cancer specific antigen (PSMA) expression in tumors through PET – computerized tomography (CT) imaging, as well as targeting PSMA lesions via radionuclide therapy (e.g. Lu-PSMA-617) or other approaches (Miyahira et al. 2020). There is a subset of CRPC that express lower levels of PSMA or lose PSMA expression in later stages of the disease, which can also be detected by PSMA PET-CT and metabolically-avid lesions confirmed with concurrent fluorodeoxyglucose (FDG) PET-CT (Thang et al. 2019). PSMA negativity or PSMA/FDG discordance on PET imaging has been associated with aggressive disease and poor prognosis (Thang et al. 2019). When tumors lose AR expression (as seen in NEPC), PSMA expression may also be lost (Bakht et al. 2018). Whether PSMA/FDG imaging can be incorporated to improve the detection of NEPC is an area of active investigation. Efforts to detect NEPC via somatostatin receptor expression using Ga-68-DOTATOC PET/CT have shown mixed results, with overall lower expression of somatostatins in NEPC compared with well-differentiated neuroendocrine tumors of the gastrointestinal tract or lung (Hope et al. 2015, Iravani et al. 2021). Other PET tracers such as those evaluating DLL3 (Sharma et al. 2017) are also under investigation.
Conclusions
In summary, NEPC is an aggressive variant of prostate cancer that most commonly develops in later stages of prostate cancer progression as a mechanism of resistance. Platinum-based chemotherapy such as carboplatin plus cabazitaxel has activity and is endorsed by NCCN guidelines, but the second line and beyond settings are major clinical challenges. While there may be certain molecular features present at initial diagnosis that may contribute toward future development of lineage plasticity or AR independence, most NEPC alterations are acquired later. Metastatic biopsy studies and recent preclinical research have identified genes and pathways that coordinate together to turn ‘off’ the AR-driven luminal prostate program and turn ‘on’ the neuroendocrine lineage. Plasticity is facilitated by genomic aberrations (e.g. combined RB1, TP53 loss), and NEPC is characterized by distinct epigenetic changes. Trials targeting emerging genes/pathways in NEPC will require careful patient selection. Metastatic biopsies are invasive and challenged by pathologic heterogeneity even within individual patients. Incorporating non-invasive biomarkers to detect molecular features of NEPC (e.g. liquid biopsies, molecular imaging) into ongoing clinical studies across the prostate cancer continuum is essential. This will help track the lineage process and facilitate prioritization, and the validation studies needed for their incorporation into future clinical trials aimed at targeting NEPC and/or reversing plasticity.
Declaration of interest
The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of this review.
Funding
H B has received research funding from Janssen, AbbVie Stemcentrx, Astellas, Eli Lilly, BMS, and Millennium and has served as advisor/consultant for Janssen, Astellas, Amgen, Astra Zeneca, Pfizer, Blue Earth, Foundation Medicine, and Sanofi Genzyme. H B and F D are supported by the Prostate Cancer Foundation and National Cancer Institute (P50 CA211024 to H B and F D, R37 CA241486-01A1 to H B). H B is also supported by the Department of Defense (W81XWH-17-1-0653) and Pussycat Foundation. F D is also supported by Accellerator Award grant by the Fondazione AIRC per la Ricerca sul Cancro (AIRC) and Cancer Research UK (CRUK) (AIRC ID 22792 and CRUK ID A26822), Fondazione Caritro and an ERC Consolidator Grant (648670).
Acknowledgement
The authors thank Gian Marco Franceschini for help with figure graphics.
References
Abida W, Cyrta J, Heller G, Prandi D, Armenia J, Coleman I, Cieslik M, Benelli M, Robinson D & Van Allen EM et al. 2019 Genomic correlates of clinical outcome in advanced prostate cancer. PNAS 116 11428–11436. (https://doi.org/10.1073/pnas.1902651116)
Aggarwal R, Huang J, Alumkal JJ, Zhang L, Feng FY, Thomas GV, Weinstein AS, Friedl V, Zhang C & Witte ON et al.2018 Clinical and genomic characterization of treatment-emergent small-cell neuroendocrine prostate cancer: a Multi-Institutional Prospective Study. Journal of Clinical Oncology 36 2492–2503. (https://doi.org/10.1200/JCO.2017.77.6880)
Aparicio AM, Harzstark AL, Corn PG, Wen S, Araujo JC, Tu SM, Pagliaro LC, Kim J, Millikan RE & Ryan C et al.2013 Platinum-based chemotherapy for variant castrate-resistant prostate cancer. Clinical Cancer Research 19 3621–3630. (https://doi.org/10.1158/1078-0432.CCR-12-3791)
Aparicio AM, Shen L, Tapia EL, Lu JF, Chen HC, Zhang J, Wu G, Wang X, Troncoso P & Corn P et al.2016 Combined tumor suppressor defects characterize clinically defined aggressive variant prostate cancer. Clinical Cancer Research 22 1520–1530. (https://doi.org/10.1158/1078-0432.CCR-15-1259)
Armstrong AJ, Luo J, Nanus DM, Giannakakou P, Szmulewitz RZ, Danila DC, Healy P, Anand M, Berry WR & Zhang T et al.2020 Prospective multicenter study of circulating tumor cell AR-V7 and taxane versus hormonal treatment outcomes in metastatic castration-resistant prostate cancer. JCO Precision Oncology 4 1285–1301. (https://doi.org/10.1200/PO.20.00200)
Baca SC, Takeda DY, Seo JH, Hwang J, Ku SY, Arafeh R, Arnoff T, Agarwal S, Bell C & O'Connor E et al.2021 Reprogramming of the FOXA1 cistrome in treatment-emergent neuroendocrine prostate cancer. Nature Communications 12 1979. (https://doi.org/10.1038/s41467-021-22139-7)
Bakht MK, Derecichei I, Li Y, Ferraiuolo RM, Dunning M, Oh SW, Hussein A, Youn H, Stringer KF & Jeong CW et al.2018 Neuroendocrine differentiation of prostate cancer leads to PSMA suppression. Endocrine-Related Cancer 26 131–146. (https://doi.org/10.1530/ERC-18-0226)
Beltran H, Rickman DS, Park K, Chae SS, Sboner A, MacDonald TY, Wang Y, Sheikh KL, Terry S & Tagawa ST et al.2011 Molecular characterization of neuroendocrine prostate cancer and identification of new drug targets. Cancer Discovery 1 487–495. (https://doi.org/10.1158/2159-8290.CD-11-0130)
Beltran H, Jendrisak A, Landers M, Mosquera JM, Kossai M, Louw J, Krupa R, Graf RP, Schreiber NA & Nanus DM et al.2016a The initial detection and partial characterization of circulating tumor cells in neuroendocrine prostate cancer. Clinical Cancer Research 22 1510–1519. (https://doi.org/10.1158/1078-0432.CCR-15-0137)
Beltran H, Prandi D, Mosquera JM, Benelli M, Puca L, Cyrta J, Marotz C, Giannopoulou E, Chakravarthi BV & Varambally S et al.2016b Divergent clonal evolution of castration-resistant neuroendocrine prostate cancer. Nature Medicine 22 298–305. (https://doi.org/10.1038/nm.4045)
Beltran H, Oromendia C, Danila DC, Montgomery B, Hoimes C, Szmulewitz RZ, Vaishampayan U, Armstrong AJ, Stein M & Pinski J et al.2018 A phase II trial of the aurora kinase A inhibitor alisertib for patients with castration resistant and neuroendocrine prostate cancer: efficacy and biomarkers. Clinical Cancer Research 25 43–51. (https://doi.org/10.1158/1078-0432.CCR-18-1912)
Beltran H, Hruszkewycz A, Scher HI, Hildesheim J, Isaacs J, Yu EY, Kelly K, Lin D, Dicker AP & Arnold JT et al.2019 The role of lineage plasticity in prostate cancer therapy resistance. Clinical Cancer Research 25 6916–6924. (https://doi.org/10.1158/1078-0432.CCR-19-1423)
Beltran H, Romanel A, Conteduca V, Casiraghi N, Sigouros M, Franceschini GM, Orlando F, Fedrizzi T, Ku SY & Dann E et al.2020 Circulating tumor DNA profile recognizes transformation to castration-resistant neuroendocrine prostate cancer. Journal of Clinical Investigation 130 1653–1668. (https://doi.org/10.1172/JCI131041)
Berchuck JE, Viscuse PV, Beltran H & Aparicio A 2021 Clinical considerations for the management of androgen indifferent prostate cancer. Prostate Cancer and Prostatic Diseases [epub]. (https://doi.org/10.1038/s41391-021-00332-5)
Bhagirath D, Liston M, Akoto T, Lui B, Bensing BA, Sharma A & Saini S 2021 Novel, non-invasive markers for detecting therapy induced neuroendocrine differentiation in castration-resistant prostate cancer patients. Scientific Reports 11 8279. (https://doi.org/10.1038/s41598-021-87441-2)
Bishop JL, Thaper D, Vahid S, Davies A, Ketola K, Kuruma H, Jama R, Nip KM, Angeles A & Johnson F et al.2017 The master neural transcription factor BRN2 is an androgen receptor-suppressed driver of neuroendocrine differentiation in prostate cancer. Cancer Discovery 7 54–71. (https://doi.org/10.1158/2159-8290.CD-15-1263)
Bluemn EG, Coleman IM, Lucas JM, Coleman RT, Hernandez-Lopez S, Tharakan R, Bianchi-Frias D, Dumpit RF, Kaipainen A & Corella AN et al.2017 Androgen receptor pathway-independent prostate cancer is sustained through FGF signaling. Cancer Cell 32 474 .e6–489.e6. (https://doi.org/10.1016/j.ccell.2017.09.003)
Brady L, Kriner M, Coleman I, Morrissey C, Roudier M, True LD, Gulati R, Plymate SR, Zhou Z & Birditt B et al.2021 Inter- and intra-tumor heterogeneity of metastatic prostate cancer determined by digital spatial gene expression profiling. Nature Communications 12 1426. (https://doi.org/10.1038/s41467-021-21615-4)
Brown LC, Halabi S, Schonhoft JD, Yang Q, Luo J, Nanus DM, Giannakakou P, Szmulewitz RZ, Danila DC & Barnett ES et al.2021 Circulating tumor cell chromosomal instability and neuroendocrine phenotype by immunomorphology and poor outcomes in men with mCRPC treated with abiraterone or enzalutamide. Clinical Cancer Research [epub]. (https://doi.org/10.1158/1078-0432.CCR-20-3471)
Chedgy EC, Vandekerkhove G, Herberts C, Annala M, Donoghue AJ, Sigouros M, Ritch E, Struss W, Konomura S & Liew J et al.2018 Biallelic tumor suppressor loss and DNA repair defects in de novo small cell prostate cancer. Journal of Pathology 246 244–253. (https://doi.org/10.1002/path.5137)
Conteduca V, Oromendia C, Eng KW, Bareja R, Sigouros M, Molina A, Faltas BM, Sboner A, Mosquera JM & Elemento O et al.2019 Clinical features of neuroendocrine prostate cancer. European Journal of Cancer 121 7–18. (https://doi.org/10.1016/j.ejca.2019.08.011)
Conteduca V, Ku SY, Puca L, Slade M, Fernandez L, Hess J, Bareja R, Vlachostergios PJ, Sigouros M & Mosquera JM et al.2020 SLFN11 expression in advanced prostate cancer and response to platinum-based chemotherapy. Molecular Cancer Therapeutics 19 1157–1164 (https://doi.org/10.1158/1535-7163.MCT-19-0926)
Conteduca V, Hess J, Yamada Y, Ku SY & Beltran H 2021 Epigenetics in prostate cancer: clinical implications. Translational Andrology and Urology [epub].(https://doi.org/10.21037/tau-20-1339)
Corn PG, Heath EI, Zurita A, Ramesh N, Xiao L, Sei E, Li-Ning-Tapia E, Tu SM, Subudhi SK & Wang J et al.2019 Cabazitaxel plus carboplatin for the treatment of men with metastatic castration-resistant prostate cancers: a randomised, open-label, phase 1–2 trial. Lancet: Oncology 20 1432–1443. (https://doi.org/10.1016/S1470-2045(1930408-5)
Cyrta J, Augspach A, De Filippo MR, Prandi D, Thienger P, Benelli M, Cooley V, Bareja R, Wilkes D & Chae SS et al.2020 Role of specialized composition of SWI/SNF complexes in prostate cancer lineage plasticity. Nature Communications 11 5549. (https://doi.org/10.1038/s41467-020-19328-1)
Dardenne E, Beltran H, Benelli M, Gayvert K, Berger A, Puca L, Cyrta J, Sboner A, Noorzad Z & MacDonald T et al.2016 N-Myc induces an EZH2-mediated transcriptional program driving neuroendocrine prostate cancer. Cancer Cell 30 563–577. (https://doi.org/10.1016/j.ccell.2016.09.005)
Drake JM, Graham NA, Lee JK, Stoyanova T, Faltermeier CM, Sud S, Titz B, Huang J, Pienta KJ & Graeber TG et al.2013 Metastatic castration-resistant prostate cancer reveals intrapatient similarity and interpatient heterogeneity of therapeutic kinase targets. PNAS 110 E4762–E4769. (https://doi.org/10.1073/pnas.1319948110).
Epstein JI, Amin MB, Beltran H, Lotan TL, Mosquera JM, Reuter VE, Robinson BD, Troncoso P & Rubin MA 2014 Proposed morphologic classification of prostate cancer with neuroendocrine differentiation. American Journal of Surgical Pathology 38 756–767. (https://doi.org/10.1097/PAS.0000000000000208)
George J, Lim JS, Jang SJ, Cun Y, Ozretić L, Kong G, Leenders F, Lu X, Fernández-Cuesta L & Bosco G et al.2015 Comprehensive genomic profiles of small cell lung cancer. Nature 524 47–53. (https://doi.org/10.1038/nature14664)
Gerdtsson AS, Setayesh SM, Malihi PD, Ruiz C, Carlsson A, Nevarez R, Matsumoto N, Gerdtsson E, Zurita A & Logothetis C et al.2021 Large extracellular vesicle characterization and association with circulating tumor cells in metastatic castrate resistant prostate cancer. Cancers 13 1056. (https://doi.org/10.3390/cancers13051056)
Gong X, Du J, Parsons SH, Merzoug FF, Webster Y, Iversen PW, Chio LC, Van Horn RD, Lin X & Blosser W et al.2019 Aurora A kinase inhibition is synthetic lethal with loss of the RB1 tumor suppressor gene. Cancer Discovery 9 248–263. (https://doi.org/10.1158/2159-8290.CD-18-0469)
Guo H, Ci X, Ahmed M, Hua JT, Soares F, Lin D, Puca L, Vosoughi A, Xue H & Li E et al.2019 ONECUT2 is a driver of neuroendocrine prostate cancer. Nature Communications 10 278. (https://doi.org/10.1038/s41467-018-08133-6)
He MX, Cuoco MS, Crowdis J, Bosma-Moody A, Zhang Z, Bi K, Kanodia A, Su MJ, Ku SY & Garcia MM et al.2021 Transcriptional mediators of treatment resistance in lethal prostate cancer. Nature Medicine 27 426–433. (https://doi.org/10.1038/s41591-021-01244-6)
Hope TA, Aggarwal R, Simko JP, VanBrocklin HF & Ryan CJ 2015 Somatostatin imaging of neuroendocrine-differentiated prostate cancer. Clinical Nuclear Medicine 40 540–541. (https://doi.org/10.1097/RLU.0000000000000776)
Horn L, Mansfield AS, Szczęsna A, Havel L, Krzakowski M, Hochmair MJ, Huemer F, Losonczy G, Johnson ML & Nishio M et al.2018 First-line atezolizumab plus chemotherapy in extensive-stage small-cell lung cancer. New England Journal of Medicine 379 2220–2229. (https://doi.org/10.1056/NEJMoa1809064)
Iravani A, Mitchell C, Akhurst T, Sandhu S, Hofman MS & Hicks RJ 2021 Molecular imaging of neuroendocrine differentiation of prostate cancer: a case series. Clinical Genitourinary Cancer [epub]. (https://doi.org/10.1016/j.clgc.2021.01.008)
Kleb B, Estécio MR, Zhang J, Tzelepi V, Chung W, Jelinek J, Navone NM, Tahir S, Marquez VE & Issa JP et al.2016 Differentially methylated genes and androgen receptor re-expression in small cell prostate carcinomas. Epigenetics 11 184–193. (https://doi.org/10.1080/15592294.2016.1146851)
Ku SY, Rosario S, Wang Y, Mu P, Seshadri M, Goodrich ZW, Goodrich MM, Labbé DP, Gomez EC & Wang J et al.2017 Rb1 and Trp53 cooperate to suppress prostate cancer lineage plasticity, metastasis, and antiandrogen resistance. Science 355 78–83. (https://doi.org/10.1126/science.aah4199)
Labrecque MP, Alumkal JJ, Coleman IM, Nelson PS & Morrissey C 2021 The heterogeneity of prostate cancers lacking AR activity will require diverse treatment approaches. Endocrine-Related Cancer 28 51–66. (https://doi.org/10.1530/ERC-21-0002)
Lapuk AV, Wu C, Wyatt AW, McPherson A, McConeghy BJ, Brahmbhatt S, Mo F, Zoubeidi A, Anderson S & Bell RH et al.2012 From sequence to molecular pathology, and a mechanism driving the neuroendocrine phenotype in prostate cancer. Journal of Pathology 227 286–297. (https://doi.org/10.1002/path.4047)
Lee JK, Phillips JW, Smith BA, Park JW, Stoyanova T, McCaffrey EF, Baertsch R, Sokolov A, Meyerowitz JG & Mathis C et al.2016 N-Myc drives neuroendocrine prostate cancer initiated from human prostate epithelial cells. Cancer Cell 29 536–547. (https://doi.org/10.1016/j.ccell.2016.03.001)
Lee JK, Bangayan NJ, Chai T, Smith BA, Pariva TE, Yun S, Vashisht A, Zhang Q, Park JW & Corey E et al.2018 Systemic surfaceome profiling identifies target antigens for immune-based therapy in subtypes of advanced prostate cancer. PNAS 115 E4473–E4482. (https://doi.org/10.1073/pnas.1802354115).
Li Z, Sun Y, Chen X, Squires J, Nowroozizadeh B, Liang C & Huang J 2015 p53 mutation directs AURKA overexpression via miR-25 and FBXW7 in prostatic small cell neuroendocrine carcinoma. Molecular Cancer Research 13 584–591. (https://doi.org/10.1158/1541-7786.MCR-14-0277-T)
Liu B, Li L, Yang G, Geng C, Luo Y, Wu W, Manyam GC, Korentzelos D, Park S & Tang Z et al.2019 PARP inhibition suppresses GR-MYCN-CDK5-RB1-E2F1 signaling and neuroendocrine differentiation in castration-resistant prostate cancer. Clinical Cancer Research 25 6839–6851. (https://doi.org/10.1158/1078-0432.CCR-19-0317)
Mahal BA, Yang DD, Wang NQ, Alshalalfa M, Davicioni E, Choeurng V, Schaeffer EM, Ross AE, Spratt DE & Den RB et al.2018 Clinical and genomic characterization of low-prostate-specific antigen, high-grade prostate cancer. European Urology 74 146–154. (https://doi.org/10.1016/j.eururo.2018.01.043)
Malihi PD, Graf RP, Rodriguez A, Ramesh N, Lee J, Sutton R, Jiles R, Ruiz Velasco C, Sei E & Kolatkar A et al.2020 Single-cell circulating tumor cell analysis reveals genomic instability as a distinctive feature of aggressive prostate cancer. Clinical Cancer Research 26 4143–4153. (https://doi.org/10.1158/1078-0432.CCR-19-4100)
McKay RR, Kwak L, Crowdis JP, Sperger JM, Zhao SG, Xie W, Werner L, Lis RT, Zhang Z & Wei XX et al.2021 Phase 2 multicenter study of enzalutamide in metastatic castration resistant prostate cancer to identify mechanisms driving resistance. Clinical Cancer Research [epub]. (https://doi.org/10.1158/1078-0432.CCR-20-4616)
Miyahira AK, Pienta KJ, Babich JW, Bander NH, Calais J, Choyke P, Hofman MS, Larson SM, Lin FI & Morris MJ et al.2020 Meeting report from the Prostate Cancer Foundation PSMA theranostics state of the science meeting. Prostate 80 1273–1296. (https://doi.org/10.1002/pros.24056)
Mounir Z, Lin F, Lin VG, Korn JM, Yu Y, Valdez R, Aina OH, Buchwalter G, Jaffe AB & Korpal M et al.2015 TMPRSS2: ERG blocks neuroendocrine and luminal cell differentiation to maintain prostate cancer proliferation. Oncogene 34 3815–3825. (https://doi.org/10.1038/onc.2014.308)
Mu P, Zhang Z, Benelli M, Karthaus WR, Hoover E, Chen CC, Wongvipat J, Ku SY, Gao D & Cao Z et al.2017 SOX2 promotes lineage plasticity and antiandrogen resistance in TP53- and RB1-deficient prostate cancer. Science 355 84–88. (https://doi.org/10.1126/science.aah4307)
Niederst MJ, Sequist LV, Poirier JT, Mermel CH, Lockerman EL, Garcia AR, Katayama R, Costa C, Ross KN & Moran T et al.2015 RB loss in resistant EGFR mutant lung adenocarcinomas that transform to small-cell lung cancer. Nature Communications 6 6377. (https://doi.org/10.1038/ncomms7377)
Nyquist MD, Corella A, Coleman I, De Sarkar N, Kaipainen A, Ha G, Gulati R, Ang L, Chatterjee P & Lucas J et al.2020 Combined TP53 and RB1 loss promotes prostate cancer resistance to a spectrum of therapeutics and confers vulnerability to replication stress. Cell Reports 31 107669. (https://doi.org/10.1016/j.celrep.2020.107669)
Oser MG, Fonseca R, Chakraborty AA, Brough R, Spektor A, Jennings RB, Flaifel A, Novak JS, Gulati A & Buss E et al.2019 Cells lacking the RB1 tumor suppressor gene are hyperdependent on aurora B kinase for survival. Cancer Discovery 9 230–247. (https://doi.org/10.1158/2159-8290.CD-18-0389)
Otto T, Horn S, Brockmann M, Eilers U, Schüttrumpf L, Popov N, Kenney AM, Schulte JH, Beijersbergen R & Christiansen H et al.2009 Stabilization of N-Myc is a critical function of aurora A in human neuroblastoma. Cancer Cell 15 67–78. (https://doi.org/10.1016/j.ccr.2008.12.005)
Papandreou CN, Daliani DD, Thall PF, Tu SM, Wang X, Reyes A, Troncoso P & Logothetis CJ 2002 Results of a phase II study with doxorubicin, etoposide, and cisplatin in patients with fully characterized small-cell carcinoma of the prostate. Journal of Clinical Oncology 20 3072–3080. (https://doi.org/10.1200/JCO.2002.12.065)
Park JW, Lee JK, Sheu KM, Wang L, Balanis NG, Nguyen K, Smith BA, Cheng C, Tsai BL & Cheng D et al.2018 Reprogramming normal human epithelial tissues to a common, lethal neuroendocrine cancer lineage. Science 362 91–95. (https://doi.org/10.1126/science.aat5749)
Puca L, Bareja R, Prandi D, Shaw R, Benelli M, Karthaus WR, Hess J, Sigouros M, Donoghue A & Kossai M et al.2018 Patient derived organoids to model rare prostate cancer phenotypes. Nature Communications 9 2404. (https://doi.org/10.1038/s41467-018-04495-z)
Puca L, Gavyert K, Sailer V, Conteduca V, Dardenne E, Sigouros M, Isse K, Kearney M, Vosoughi A & Fernandez L et al.2019 Delta-like protein 3 expression and therapeutic targeting in neuroendocrine prostate cancer. Science Translational Medicine 11 eaav0891. (https://doi.org/10.1126/scitranslmed.aav0891)
Quaglia F, Krishn SR, Daaboul GG, Sarker S, Pippa R, Domingo-Domenech J, Kumar G, Fortina P, McCue P & Kelly WK et al.2020 Small extracellular vesicles modulated by αVβ3 integrin induce neuroendocrine differentiation in recipient cancer cells. Journal of Extracellular Vesicles 9 1761072. (https://doi.org/10.1080/20013078.2020.1761072)
Reina-Campos M, Linares JF, Duran A, Cordes T, L'Hermitte A, Badur MG, Bhangoo MS, Thorson PK, Richards A & Rooslid T et al.2019 Increased serine and one-carbon pathway metabolism by PKCλ/ι deficiency promotes neuroendocrine prostate cancer. Cancer Cell 35 385 .e9–400.e9. (https://doi.org/10.1016/j.ccell.2019.01.018)
Rotinen M, You S, Yang J, Coetzee SG, Reis-Sobreiro M, Huang WC, Huang F, Pan X, Yáñez A & Hazelett DJ et al.2018 ONECUT2 is a targetable master regulator of lethal prostate cancer that suppresses the androgen axis. Nature Medicine 24 1887–1898. (https://doi.org/10.1038/s41591-018-0241-1)
Saunders LR, Bankovich AJ, Anderson WC, Aujay MA, Bheddah S, Black K, Desai R, Escarpe PA, Hampl J & Laysang A et al.2015 A DLL3-targeted antibody-drug conjugate eradicates high-grade pulmonary neuroendocrine tumor-initiating cells in vivo. Science Translational Medicine 7 302ra136. (https://doi.org/10.1126/scitranslmed.aac9459)
Scher HI, Graf RP, Schreiber NA, McLaughlin B, Jendrisak A, Wang Y, Lee J, Greene S, Krupa R & Lu D et al.2017 Phenotypic heterogeneity of circulating tumor cells informs clinical decisions between AR signaling inhibitors and taxanes in metastatic prostate cancer. Cancer Research 77 5687–5698. (https://doi.org/10.1158/0008-5472.CAN-17-1353)
Sella A, Konichezky M, Flex D, Sulkes A & Baniel J 2000 Low PSA metastatic androgen-independent prostate cancer. European Urology 38 250–254. (https://doi.org/10.1159/000020289)
Sharma SK, Pourat J, Abdel-Atti D, Carlin SD, Piersigilli A, Bankovich AJ, Gardner EE, Hamdy O, Isse K & Bheddah S et al.2017 Noninvasive interrogation of DLL3 expression in metastatic small cell lung cancer. Cancer Research 77 3931–3941. (https://doi.org/10.1158/0008-5472.CAN-17-0299)
Shukla S, Cyrta J, Murphy DA, Walczak EG, Ran L, Agrawal P, Xie Y, Chen Y, Wang S, Zhan Y, et al.2017 Aberrant activation of a gastrointestinal transcriptional circuit in prostate cancer mediates castration resistance. Cancer Cell 2017 32 792–806.e7. (https://doi.org/10.1016/j.ccell.2017.10.008)
Smith M, De Bono J, Sternberg C, Le Moulec S, Oudard S, De Giorgi U, Krainer M, Bergman A, Hoelzer W & De Wit R et al.2016 Phase III study of cabozantinib in previously treated metastatic castration-resistant prostate cancer: COMET-1. Journal of Clinical Oncology 34 3005–3013. (https://doi.org/10.1200/JCO.2015.65.5597)
Spratt DE, Alshalalfa M, Fishbane N, Weiner AB, Mehra R, Mahal BA, Lehrer J, Liu Y, Zhao SG & Speers C et al.2019 Transcriptomic heterogeneity of androgen receptor activity defines a de novo low AR-active subclass in treatment naïve primary prostate cancer. Clinical Cancer Research 25 6721–6730. (https://doi.org/10.1158/1078-0432.CCR-19-1587)
Thang SP, Violet J, Shandhu S, Iravani A, Akhurst T, Kong G, Kumar A, Murphy DG, Wiliams SG & Hicks RJ et al.2019 Poor outcomes for patients with metastatic castration-resistant prostate cancer with low prostate-specific membrane antigen (PSMA) expression deemed ineligible for 177 Lu-labelled PSMA radioligand therapy. European Urology Oncology 2 670–676. (https://doi.org/10.1016/j.euo.2018.11.007)
Thomas A, Takahashi N, Rajapakse VN, Zhang X, Sun Y, Ceribelli M, Wilson KM, Zhang Y, Beck E, Sciuto L, et al.2021 Therapeutic targeting of ATR yields durable regressions in small cell lung cancers with high replication stress. Cancer Cell 39 566 .e7–579.e7. (https://doi.org/10.1016/j.ccell.2021.02.014)
Thompson JA, Grunert F & Zimmermann W 1991 Carcinoembryonic antigen gene family: molecular biology and clinical perspectives. Journal of Clinical Laboratory Analysis 5 344–366. (https://doi.org/10.1002/jcla.1860050510)
Tiwari R, Manzar N, Bhatia V, Yadav A, Nengroo MA, Datta D, Carskadon S, Gupta N, Sigouros M, Khani F, et al.2020 Androgen deprivation upregulates SPINK1 expression and potentiates cellular plasticity in prostate cancer. Nature Communications 11 384. (https://doi.org/10.1038/s41467-019-14184-0)
Ulz P, Perakis S, Zhou Q, Moser T, Belic J, Lazzeri I, Wölfler A, Zebisch A, Gerger A, Pristauz G, et al.2019 Inference of transcription factor binding from cell-free DNA enables tumor subtype prediction and early detection. Nature Communications 10 4666. (https://doi.org/10.1038/s41467-019-12714-4)
Unno K, Chalmers ZR, Pamarthy S, Vatapalli R, Rodriguez Y, Lysy B, Mok H, Sagar V, Han H & Yoo YA et al.2021 Activated ALK cooperates with N-Myc via Wnt/β-catenin signaling to induce neuroendocrine prostate cancer. Cancer Research 81 2157–2170. (https://doi.org/10.1158/0008-5472.CAN-20-3351)
Xu K, Wu ZJ, Groner AC, He HH, Cai C, Lis RT, Wu X, Stack EC, Loda M & Liu T et al.2012 EZH2 oncogenic activity in castration-resistant prostate cancer cells is polycomb-independent. Science 338 1465–1469. (https://doi.org/10.1126/science.1227604)
Zhang X, Coleman IM, Brown LG, True LD, Kollath L, Lucas JM, Lam HM, Dumpit R, Corey E & Chéry L et al.2015 SRRM4 expression and the loss of REST activity may promote the emergence of the neuroendocrine phenotype in castration-resistant prostate cancer. Clinical Cancer Research 21 4698–4708. (https://doi.org/10.1158/1078-0432.CCR-15-0157)
Zhang W, Liu B, Wu W, Li L, Broom BM, Basourakos SP, Korentzelos D, Luan Y, Wang J & Yang G et al.2018 Targeting the MYCN-PARP-DNA damage response pathway in neuroendocrine prostate cancer. Clinical Cancer Research 24 696–707. (https://doi.org/10.1158/1078-0432.CCR-17-1872)
Zhao SG, Chen WS, Li H, Foye A, Zhang M, Sjöström M, Aggarwal R, Playdle D, Liao A & Alumkal JJ et al.2020 The DNA methylation landscape of advanced prostate cancer. Nature Genetics 52 778–789. (https://doi.org/10.1038/s41588-020-0648-8)
