The prognostic value of androgen receptor (AR) in HER2-enriched metastatic breast cancer

in Endocrine-Related Cancer
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  • 1 Department of Medical Oncology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou, People’s Republic of China

Correspondence should be addressed to Z Yuan: yuanzhy@sysucc.org.cn

*(X Wang, X Bi and Z Huang contributed equally to this work)

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The significance of androgen receptor (AR) in metastatic breast cancer (MBC) remains unclear, and it is still largely unknown how AR expression level influences HER2-positive tumors. This study aimed to investigate the prognostic and predictive value of AR in HER2-enriched MBC. Primary and/or paired metastatic tumors of 304 patients with pathologically confirmed HER2-enriched MBC were collected and immunohistochemically assessed for AR expression. The associations of AR and other clinicopathological characteristics were compared using the Chi-square test. Progression-free survival (PFS) and overall survival (OS) were calculated using the Kaplan–Meier method and log-rank test. Cox regression analysis was used to determine independent prognostic factors. AR-positivity with a cut-off value of 10% was observed in 237 (78.0%) cases and was associated with longer PFS, 13.2 months, as compared to that of 8.2 months (P = 0.004) in patients with AR-negativity. Moreover, a significant increase in the 5-year OS rate (65.3% vs 36.2%, P < 0.001) was also observed for patients with AR-positive tumors. Cox regression analysis identified AR-positivity as an independent prognostic factor of both PFS (hazard ratio = 0.71, P = 0.039) and OS (HR = 0.53, P = 0.013). Additionally, for those who received first-line Trastuzumab therapies, prolonged PFS (15.8 months vs 8.2 months, P = 0.005) and 5-year OS rate (66.2% vs 26.2%, P = 0.009) were observed in AR-positive tumors compared to AR-negative ones. In conclusion, AR was identified as an independent prognostic factor for favorable PFS and OS and could also predict the efficacy of first-line Trastuzumab treatment in patients with HER2-enriched MBC.

Abstract

The significance of androgen receptor (AR) in metastatic breast cancer (MBC) remains unclear, and it is still largely unknown how AR expression level influences HER2-positive tumors. This study aimed to investigate the prognostic and predictive value of AR in HER2-enriched MBC. Primary and/or paired metastatic tumors of 304 patients with pathologically confirmed HER2-enriched MBC were collected and immunohistochemically assessed for AR expression. The associations of AR and other clinicopathological characteristics were compared using the Chi-square test. Progression-free survival (PFS) and overall survival (OS) were calculated using the Kaplan–Meier method and log-rank test. Cox regression analysis was used to determine independent prognostic factors. AR-positivity with a cut-off value of 10% was observed in 237 (78.0%) cases and was associated with longer PFS, 13.2 months, as compared to that of 8.2 months (P = 0.004) in patients with AR-negativity. Moreover, a significant increase in the 5-year OS rate (65.3% vs 36.2%, P < 0.001) was also observed for patients with AR-positive tumors. Cox regression analysis identified AR-positivity as an independent prognostic factor of both PFS (hazard ratio = 0.71, P = 0.039) and OS (HR = 0.53, P = 0.013). Additionally, for those who received first-line Trastuzumab therapies, prolonged PFS (15.8 months vs 8.2 months, P = 0.005) and 5-year OS rate (66.2% vs 26.2%, P = 0.009) were observed in AR-positive tumors compared to AR-negative ones. In conclusion, AR was identified as an independent prognostic factor for favorable PFS and OS and could also predict the efficacy of first-line Trastuzumab treatment in patients with HER2-enriched MBC.

Introduction

Breast cancer is a highly heterogeneous disease composed of biological subgroups (Carey et al. 2006, Kravchenko et al. 2011). Current standard treatment options are based on the expression of estrogen receptor alpha (ERa), progesterone receptor (PR), and human EGF receptor 2 (HER2) (NCCN 2018). HER2-enriched breast cancer accounts for 20% of patients with early stage and is associated with high risk of recurrence and poor prognosis (Arteaga et al. 2011), and therefore acquiring comprehensive information for metastatic tumors is needed to improve clinical outcomes.

Similar to ER and PR, androgen receptor (AR) is a member of the steroid nuclear receptor family (Basile et al. 2017), playing an important role in the carcinogenesis of breast cancer, particularly in the metastatic setting, and it has recently emerged as another promising therapeutic target. AR has been detected in up to 90% of primary breast cancers and up to 75% of metastatic lesions (Lea et al. 1989, Moinfar et al. 2003, Park et al. 2010, Honma et al. 2012). Previous studies, including three meta-analyses, have demonstrated an association between AR expression and treatment response as well as favorable prognosis in early breast cancer (Loibl et al. 2011, Qu et al. 2013, Vera-Badillo et al. 2014, Hilborn et al. 2016, Bozovic-Spasojevic et al. 2017). However, given the high degree of heterogeneity in breast cancer, the role of AR should be explored in the context of different subtypes (McNamara et al. 2014). In ER-positive tumors, AR-positive identifies a subgroup of patients with better outcomes, while the AR/ER ratio ≥2 represents a worse marker for prognosis (Aleskandarany et al. 2016, Rangel et al. 2018). In ER-negative tumors, investigation of AR seems more applicable since they lack response to current standard endocrine therapy. It has been reported that 32% of HER2-enriched breast cancer patients expressed AR (Aleskandarany et al. 2016). Moreover, the relationships between AR and HER2 seems to be associated with ER status, as a statistically significant association between AR and HER2 was observed in ER-negative tumors but not in ER-positive tumors (Chia et al. 2015). In addition, an in vitro study proposed that AR, activated by either androgen or Wnt7B, was able to bind to FOXA1 and β-catenin and thus activating HER2 and HER3 downstream. The positive feedback between AR and HER2 promotes the proliferation of breast cancer cells (Ni et al. 2011). However, whether AR carries prognostic significance in HER2-positive breast tumors has been rarely reported and remains unclear (Vera-Badillo et al. 2014), not to mention in the metastatic settings. Moreover, the role of AR in determining efficacy for which HER2-directed regimens warrants proper evaluation, especially for Trastuzumab as one of the most effective and commonly used regimens.

We performed this study to better understand the significance of AR in HER2-enriched metastatic breast cancer (MBC) and to help identify patients who could potentially benefit from AR-inhibitors. We hypothesized that tumors with AR-positive status would demonstrate an improved outcome in patients with HER2-enriched MBC.

Materials and methods

Patients and case selection

The study was conducted according to the REporting recommendations for tumour MARKer prognostic studies (REMARK) (McShane et al. 2005). Database of Sun Yat-sen University Cancer Center (Guangzhou, China) from January 1st, 2000 to May 1st, 2019 was screened. Patients with pathologically confirmed HER2-enriched (ER-negative/PR-negative/HER2-positive) breast cancer with local or distant relapse who were not eligible to locoregional treatment were selected. Patients were also required to have available primary and/or relapsed tumor tissue.

Clinicopathological features and treatment modalities were reviewed and collected from our hospital’s digital medical records database. Patients characteristics: (1) age at diagnosis and (2) history of surgery. Tumors data: (1) pathological histotype (ductal, lobular, other, and unknown); (2) histologic grade of primary tumor; (3) tumor stage; (4) metastases at diagnosis (M0–1); (5) ER, PR, HER2, Ki67, and AR status of primary tumor and/or metastases (biomarker evaluated on metastatic tissue when a metastatic biopsy was performed, biomarker assessed on primary tumors when metastatic biopsy was not available); (6) number of metastases; and (7) location of distant metastases. Tumors were staged according to the American Joint Committee on Cancer (AJCC) Cancer Staging Manual 8th Edition (Giuliano et al. 2017). Treatment and outcome: (1) previous adjuvant chemotherapy; (2) previous adjuvant anti-HER2 therapy; (3) previous adjuvant radiotherapy; (4) first-line anti-HER2 regimen; (5) progression-free survival (PFS), defined as the duration from the date of first-line anti-HER2 therapy to the date of tumor progression, death from any cause, or the last follow-up; and (6) overall survival (OS), defined as the duration from the date of diagnosis of breast cancer until the date of death from any cause or the last follow-up.

A total of 304 patients were included in the present study, all of whom had been assessed for AR expression on their primary tumor and/or paired metastases samples. Given the accessibility and availability of specimens, AR was measured on metastases if biopsies of metastases were available or on primary samples if biopsies of metastases had not been performed. The study protocol was approved by the Academic and Ethics Committee of Sun Yat-sen University Cancer Center (approval no. B2018-100-01). Informed consent from all patients had been obtained at their first medical visit.

Biomarker assessment

ER, PR, HER2, Ki67, and AR status of the primary tumor, metastases, or both were evaluated for all patients enrolled. All biomarkers were assessed by immunohistochemistry staining in the Department of Pathology of Sun Yat-sen University Cancer Center. Tumor tissues obtained in the surgery were fixed in neutral buffed formalin and embedded in paraffin. The corresponding original hematoxylin-eosin stained sections and the expression of biomarkers were reviewed and evaluated independently by two experienced pathologists blinded to the patients’ clinical status. Disagreement was resolved by consensus after joint review.

Immunostainings for ER, PR, and Ki67 were evaluated according to the ASCO guidelines (Wolff et al. 2013). Evaluation of immunostaining or in situ hybridization of HER2 is accorded to the ASCO guidelines. Immunostainings of all five biomarkers were performed using the Ventana Benchmark XT® staining system (Ventana Medical Systems, Tucson, AZ, USA) with the Optiview® DAB Detection Kit (Ventana Medical Systems, Tucson, AZ, USA). ER (790-4324, Ventana Medical Systems, Tucson, AZ, USA), PR (790-2223, Ventana Medical Systems, Tucson, AZ, USA), HER2 (790-2991, 4B5, Ventana Medical Systems, Tucson, AZ, USA), Ki67 (IS62630-2, Dako, Santa Clara, California), and AR (ZA-0554, Zsbio, Beijing, China) antibodies were utilized. ASCO-CAP guidelines were used in the evaluation of ER, PR, HER2, and Ki67 immunostaining. ER and PR were considered positive when ≥1% of cells were stained. For Ki67, the positive percentage of its immunohistochemical staining was noted. Ki67 was defined as high when the percentage of stained cells was ≥20% and low when <20%. For HER2, evaluation by immunostaining was expressed as 0–3+ as recommended scale. HER2 was considered positive when cases scored 3+. Fluorescent in situ hybridization (Ventana Medical Systems, Tucson, AZ, USA) was performed in cases scoring 2+. HER2 gene/chromosome 17 centromere ratio ≥2 or average HER2 gene copy number per cell ≥6 was considered HER2-positive. Regarding AR ≥10%, stained cells in nucleus were considered positive.

Statistical analysis

All clinicopathological characteristics were described according to descriptive statistics. Concordance of AR status was defined as either positive/negative in both primary tumors and paired metastases, while discordance as positive at one site and negative at the other or vice versa. Concordance rate and discordance rate were calculated as the proportion of AR status concordant or discordant cases.

The associations between AR expression and other clinicopathological characteristics were compared using the Chi-square test and Spearman-rank correlation test. A two-sided exact binominal 95% CI was also calculated. Kaplan–Meier method was used to estimate the cumulative survival rate and to plot the PFS and OS curves. The log-rank test was used to compare the differences between the study arms. Univariate Cox regression analysis was used to identify prognostic factors associated with PFS and OS. Multivariate Cox proportional hazards model with a forward stepwise selection of significant univariate factors or other confounding variables with clinical significance considered by the researchers was used to determine independent prognostic factors. Hazard ratios (HR) and 95% CI were presented. A two-tailed P value of <0.05 was considered as having statistical significance. All statistical analyses were conducted with the SPSS statistical software package (version 23.0, IBM).

Results

Patients’ characteristics

A total of 304 patients with HER2-enriched MBC were included in the study, after application of the selection criteria (Fig. 1). Biological characteristics were analyzed in primary tumors, metastatic lesions, or both for 169, 135, and 24 cases, respectively. Patients and tumor clinicopathological features are detailed in Table 1.

Figure 1
Figure 1

Study flow diagram of the study.

Citation: Endocrine-Related Cancer 27, 4; 10.1530/ERC-19-0315

Table 1

Characteristics of 304 patients enrolled in the present study.

VariablesaTotalAR < 10% (%)AR ≥ 10% (%)P
Number of cases (%)30467 (22.0)237 (78.0)
Median age at diagnosis, years (range)48 (23–81)43 (28–77)49 (26–78)0.006
Surgery, n (%)
 Yes271 (89.1)63 (94.0)208 (87.8)0.146
 No33 (10.9)4 (6.0)29 (12.2)
Tumor stage, n (%)
 I19 (6.3)4 (6.0)15 (6.3)0.502
 II52 (17.1)10 (14.9)42 (17.7)
 III129 (42.4)34 (50.7)95 (40.1)
 IV87 (28.6)14 (20.9)73 (30.8)
 Unknown17 (5.6)5 (7.5)12 (5.1)
Histotype, n (%)
 Ductal266 (87.5)60 (89.6)206 (86.9)0.738
 Lobular3 (1.0)0 (0.0)3 (1.3)
 Other13 (4.3)3 (4.4)10 (4.2)
 Unknown22 (7.2)4 (6.0)18 (7.6)
Histologic grade of primary tumor, n (%)
 11 (0.3)0 (0.0)1 (0.4)0.276
 2118 (38.8)24 (35.8)94 (39.7)
 3119 (39.1)32 (47.8087 (36.7)
 Unknown66 (21.7)11 (16.4)55 (23.2)
Previous adjuvant chemotherapyb, n (%)
 Yes191 (88.0)45 (86.5)146 (88.5)0.978
 No20 (9.2)5 (9.6)15 (9.1)
 Unknown6 (2.8)2 (3.9)4 (2.4)
Previous adjuvant anti-HER2 therapyb, n (%)
 Yes73 (33.6)16 (30.8)81 (49.1)0.616
 No143 (65.9)36 (69.2)71 (43.0)
 Unknown1 (0.5)0 (0.0)13 (7.9)
Previous adjuvant radiotherapyb, n (%)
 Yes94 (43.3)26 (50)107 (64.8)0.958
 No107 (49.3)23 (44.2)57 (34.5)
 Unknown16 (7.4)3 (5.8)1 (0.6)
Number of metastases, n (%)
 1156 (51.3)33 (49.3)123 (51.9)0.220
 274 (24.3)14 (20.9)60 (25.3)
 ≥374 (24.3)20 (29.8)54 (22.8)
Location of distant metastases or local recurrence, n (%)
 Local recurrence only23 (7.6)5 (7.5)18 (7.6)0.971
 Lung103 (33.9)29 (43.3)74 (31.2)0.066
 Liver107 (35.2)21 (31.3)86 (36.3)0.455
 Bone98 (32.2)20 (29.9)78 (32.9)0.637
 Brain43 (14.1)10 (14.9)32 (13.5)0.766
 Distant lymph node139 (45.7)29 (43.3)110 (46.4)0.650
 Other40 (13.2)14 (20.9)26 (11.0)0.028
First-line anti-HER2 therapy, n (%)
 Yes215 (70.7)42 (62.7)173 (73.0)0.102
 Type of first-line anti-HER2 therapy, n (%)
  Trastuzumab153 (71.2)31 (46.3)122 (70.5)0.452
  Lapatinib18 (8.4)3 (4.5)15 (8.7)0.571
  T-DM15 (2.3)2 (3.0)3 (1.7)0.329
  Pyrotinib1 (0.5)0 (0.0)1 (0.6)0.595
  Trastuzumab + Lapatinib28 (13.0)5 (7.5)23 (13.3)0.576
  Trastuzumab + Pertuzumab10 (4.7)1 (1.5)9 (5.2)0.351
 No89 (29.3)25 (37.3)64 (27.0)

aBiomarker measured on the metastatic sample when metastatic biopsies were available or on primary tumor when biopsies of metastasis had not been performed. bData were calculated based on 217 patients who were first diagnosed as early breast cancer (EBC). The rest of the 87 patients were excluded from this category because they were MBC at first diagnosis, and therefore they received salvage therapy rather than adjuvant therapy.

AR, androgen receptor; HER2, human EGF receptor 2; T-DM1, trastuzumab emtansine.

The median age at diagnosis was 48 years (range 23–81 years). Initial tumor staging was distributed as follows: stage I in 19 (6.3%) cases, stage II in 52 (17.1%) cases, and stage III in 129 (42.4%) cases. Eighty-seven (28.6%) patients had metastatic disease at presentation, and among the rest of the 217 patients that were non-metastatic at first diagnosis, 73 (33.6%) cases had received adjuvant HER2-directed therapy. Of all 304, 215 (70.7%) received first-line anti-HER2-based therapy after relapse, including trastuzumab (84.9%), lapatinib (20.4%), trastuzumab emtansine (T-DM1) (2.2%), pertuzumab (4.4%), and pyrotinib (0.4%) for metastatic disease. Thirty-nine (12.8%) patients had undergone one or more lines of chemotherapy for metastatic diseases before adding anti-HER2 treatment, whereas 43 (14.1%) patients had never received any regimen targeting HER2 (Table 1).

Biomarker distribution

All patients included were HER2-enriched subtype MBC, with AR assessment in 169 (55.6%) cases on primary tumors, 135 (44.4%) cases on metastases, and 24 (7.9%) on both sites (Fig. 2 and Table 2). Overall, AR-positivity was observed in 237 (78.0%) cases. In addition, we found that AR status was negative in 40 (59.7%) samples of primary tumors and in 27 (40.3%) samples of metastases (Fig. 3A and Table 2).

Figure 2
Figure 2

Representative images of AR staining in three cases. AR-negative (A, 100× magnification; B, 200× magnification), AR-positive with nuclear staining of 10% (C, 100× magnification; D, 200× magnification), and AR-positive with nuclear staining >90% (E, 100× magnification; F, 200× magnification). AR, androgen receptor. A full color version of this figure is available at https://doi.org/10.1530/ERC-19-0315.

Citation: Endocrine-Related Cancer 27, 4; 10.1530/ERC-19-0315

Figure 3
Figure 3

Distribution and discordance rate of AR expression level. (A) Distribution of AR status on primary tumor (red, 169 cases), metastatic lesions (blue, 135 cases), and both sites (green, 24 cases) in 304 patients with HER2-enriched MBC. (B) The percentage change of AR staining level from primary tumor to paired metastatic lesions for 24 cases. AR, androgen receptor. A full color version of this figure is available at https://doi.org/10.1530/ERC-19-0315.

Citation: Endocrine-Related Cancer 27, 4; 10.1530/ERC-19-0315

Table 2

Biomarker distribution and overall discordance rate.

TotalPrimary tumorMetastases
AR statusa304169 (55.6)135 (44.4)
 <10%67 (22.0)40 (23.7)27 (20.0)
 ≥10%237 (78.0)129 (76.3)108 (80.0)
Overall discordance rate (95% CI)33.3 (13.0–53.7)

aBiomarker measured on the metastatic sample when metastatic biopsies were available or on primary tumor when biopsies of metastasis had not been performed.

AR, androgen receptor.

Moreover, among 24 cases of paired primary tumor and confirmed metastases, 21 (87.5%) cases had change in AR protein expression level and eight (33.3%) cases had conversion in AR status (from negative to positive or positive to negative, cut-off at 10% for AR-positivity; Fig. 3A and B). The overall discordance rate was 33.3% (95% CI: 13.0–53.7%, Table 2).

AR-positivity has an independent prognostic significance for favorable clinical outcome

At a median follow-up of 33.9 months (range 20.9–54.6), the median PFS was 11.8 months (95% CI: 10.1–13.4) for the entire cohort.

AR-positivity was associated with improved clinical outcome in patients with HER2-enriched subtype MBC. Our results showed a significantly longer median PFS of 13.2 months (95% CI: 11.6–14.9) in patients with AR ≥10%, compared to that of 8.2 months (95% CI: 5.8–10.7, P = 0.004, Fig. 4A) in patients with AR < 10%.

Figure 4
Figure 4

Progression-free survival (A) and overall survival (B) in 304 patients with HER2-enriched MBC were calculated using the Kaplan–Meier method, respectively. The log-rank test was used to compare the differences between the study arms. Cut-off at 10% for AR-positivity. AR, androgen receptor. A full color version of this figure is available at https://doi.org/10.1530/ERC-19-0315.

Citation: Endocrine-Related Cancer 27, 4; 10.1530/ERC-19-0315

The 5-year OS rate was 58.9% for the whole cohort. Compared with AR-negative patients, a significantly increased 5-year OS rate (65.3% vs 36.2%, P < 0.001, Fig. 4B) was also found in patients with AR-positive tumors.

In Cox univariate models, AR status, number of metastases, and first-line anti-HER2 therapy were related to PFS, while AR status, surgery, previous adjuvant anti-HER2 therapy, and first-line anti-HER2 therapy were associated with OS (Table 3). In addition, multivariate analysis identified that only AR status remained an independent prognostic factor for both PFS (HR = 0.71, 95% CI: 0.51–0.98, P = 0.039) and OS (HR = 0.53, 95% CI: 0.32–0.87, P = 0.013, Table 4) in the HER2-enriched population.

Table 3

Results of the univariate Cox-regression analysis.

VariablesaNO.PFSOS
HR (95% CI)PHR (95% CI)P
Age (year)
 ≤501791.000.7321.000.100
 >501250.95 (0.73–1.25)1.42 (0.94–2.15)
Surgery
 Yes2710.68 (0.44–1.05)0.0780.432 (0.228–0.818)0.010
 No331.001.00
Tumor stage
 I–II771.000.1271.000.179
 III–IV2091.27 (0.94–1.71)1.41 (0.854–2.33)
Histologic grade of primary tumor
 G1–211910.4731.000.724
 G31191.12 (0.83–1.51)1.09 (0.68–1.74)
AR status
 <10%671.0000.0051.000.002
 ≥10%2370.64 (0.47–0.87)0.50 (0.33–0.78)
Ki67 status
 <20%351.000.623 1.000.533
 ≥20%2590.91 (0.61–1.35)0.87 (0.56–1.35)
Previous adjuvant chemotherapy
 Yes1921.71 (0.97–3.03)0.0652.10 (0.76–5.77)0.151
 No1061.001.00
Previous adjuvant anti-HER2 therapy
 Yes731.16 (0.82–1.65)0.4070.49 (0.28–0.88)0.017
 No14311.00
Metastases (at diagnosis)
 Yes870.93 (0.70–1.25)0.6371.03 (0.62–1.69)0.918
 No2171.001.00
Number of metastases
 11331.000.0281.000.759
 2741.39 (1.01–1.92)1.20 (0.73–1.97)
 ≥3741.52 (1.10–2.10)1.14 (0.69–1.89)
First-line anti-HER2 therapy
 Yes2150.56 (0.42–0.75)<0.0010.51 (0.33–0.79)0.002
 No8911.00

aBiomarker measured on the metastatic sample when a metastatic biopsy was available or on primary tumor when a biopsy of metastasis had not been performed.

AR, androgen receptor; HER2, human EGF receptor 2; HR, hazard ratio.

Table 4

Results of the multivariate Cox-regression analysis.

VariablesaNO.PFSOS
HR (95% CI)PHR (95% CI)P
AR status
 <10%671.000.0391.000.013
 ≥10%2370.71 (0.51–0.98)0.53 (0.32–0.87)
Surgery
 Yes2710.7 (0.2–2.8)0.597
 No33
Number of metastases
 11331.000.143
 2741.29 (0.93–1.80)
 ≥3741.36 (0.98–1.91)
Previous adjuvant anti-HER2 therapy
 Yes730.60 (0.33–1.09)0.094
 No1431.00
First-line anti-HER2 therapy
 Yes2150.61 (0.46–0.82)<0.0010.72 (0.43–1.20)0.208
 No791.001.00

aBiomarker measured on the metastatic sample when a metastatic biopsy was available or on primary tumor when a biopsy of metastasis had not been performed.

AR, androgen receptor; HER2, human EGF receptor 2; HR, hazard ratio.

AR predicts benefit from first-line Trastuzumab treatment in patients with HER2-enriched tumors

AR-positivity was significantly associated with better response to first-line Trastuzumab treatment. For those who received first-line Trastuzumab therapies, both prolonged PFS and OS were observed in patients with AR-positive tumors (PFS: 15.8 months, 95% CI: 13.6–17.9; 5-year OS rate: 66.2%, 95%CI: 57.5–73.1%) compared to AR-negative ones (PFS: 8.2 months, 95% CI: 5.0–11.4, P = 0.005, Fig. 5A; 5-year OS rate: 26.6%, 95% CI: 0.3–52.8%, P = 0.009, Fig. 5B).

Figure 5
Figure 5

Progression-free survival (A) and overall survival (B) were calculated using the Kaplan–Meier method for patients who received first-line Trastuzumab treatment, respectively. The log-rank test was used to compare the differences between the study arms. Cut-off at 10% for AR-positivity. AR, androgen receptor. A full color version of this figure is available at https://doi.org/10.1530/ERC-19-0315.

Citation: Endocrine-Related Cancer 27, 4; 10.1530/ERC-19-0315

Discussion

Here, we presented the findings of a retrospective cohort of HER2-enriched subtype MBC. Our findings showed that AR-positive status was significantly and independently associated with improved survival. Moreover, AR status was identified as a useful predictor for favorable response to first-line Trastuzumab treatment.

In the present study, we found a high prevalence of AR expression of 78.0%, using 10% as the cut-off value. In contrast, AR expression was detected in 32% of HER2-enriched tumors in previous report (Aleskandarany et al. 2016). The difference regarding percentages of AR-positive tumors may depend on sample size, ethics, different choice of antibodies, different choice of paraffin-embedded or frozen sections, and varying cut-off values (Moinfar et al. 2003, Pusztai et al. 2010, Collins et al. 2011).

Consistent with some previous studies focusing on hormone receptor (HR)-positive and triple negative (TN) early breast cancer (Vera-Badillo et al. 2014, Bozovic-Spasojevic et al. 2017), AR-positivity in the present study also served as an independent prognostic indicator of improved survival which, to the best of our knowledge, was first reported in HER2-enriched MBC. As our results demonstrate that AR expression carries prognostic value, we recommend that patients with HER2-enriched MBC should have AR status reevaluated on metastasis or recurrence in order to obtain comprehensive information.

In addition, this is the first study to our knowledge to investigate the predictive value of AR in efficacy of first-line Trastuzumab treatment. Trastuzumab is one of the most effective HER2-directed regimens that had remarkably improved patients’ outcome (Slamon et al. 2001, Romond et al. 2005). However, many patients with pathological or FISH confirmed HER2-positive tumor do not respond to it de novo or acquire drug resistance within 1–2 years, suggesting that HER2 overexpression is not the sole determinant of Trastuzumab response (Arteaga et al. 2011, Stern 2012). We analyzed the cohort (n = 153) receiving Trastuzumab as first-line therapy and found that cases demonstrating AR-positivity had improved PFS and OS. Thus, AR status should be detected as a complement for predicting efficacy of Trastuzumab. Moreover, we acknowledge that the study was not powered to determine whether AR status could predict response to Lapatinib (n = 18), T-DM1 (n = 5), Pyrotinib (n = 1), Trastuzumab + Lapatinib (n = 28), and Trastuzumab + Pertuzumab (n = 10) therapies, as most of the patients received Trastuzumab in the cohort. Therefore, further directed studies could be designed to better explore this issue.

AR-inhibitors have relatively mild toxicity and high compliance. This promising therapeutic strategy can produce clinical benefits, particularly for those who could not tolerate chemotherapy or have experienced chemotherapy failure/resistance (Gucalp et al. 2013, Barton et al. 2015). Moreover, previous studies have reported AR-mediated trastuzumab resistance in breast cancer cell lines and suggested that dual inhibition of AR and HER2 could recover drug sensitivity and exert a synergistic effect (Gordon et al. 2017). Currently, a novel single-arm phase II clinical trial (NCT02091960) exploiting anti-AR in combination with anti-HER2 for AR-positive/HER2-positive/HR-negative MBC is underway. The findings of this study may provide additional implications for clinical trials.

The limitations of the present study are as follows. Unlike the current standard for ER and PR, which used 1% as the cut-off value, the optimal cut-off value for AR status still remains in dispute, varying from >1% to >75% (Agoff et al. 2003, Peters et al. 2009, Asano et al. 2017, Elebro et al. 2017). In our study, the threshold of 10% showed independent prognostic and predictive significance, and therefore it can better stratify patients, whereas 1% did not. Also, limitations of the study lie in its retrospective feature and modest sample size of AR-negative cases. Therefore, further prospective studies are needed to confirm these results. In addition, unveiling the complicated interactions between AR and the HER2 signaling pathway will further help utilizing AR as an attractive therapeutic target in HER2-enriched MBC.

Conclusion

We have demonstrated that AR-positivity is an independent prognostic factor for prolonged PFS and OS in patient with HER2-enriched MBC. AR overexpression is also identified as a predictor for response to first-line Trastuzumab treatment. We recommend that patients with HER2-enriched MBC to have their primary and paired metastatic tumors tested for AR status.

Declaration of interest

The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

Funding

This work did not receive any specific grant from any funding agency in the public, commercial, or not-for-profit sector.

Data availability

The datasets generated and/or analyzed in the current study are available from the Research Data Deposit (www.researchdata.org.cn). Data are also available from the corresponding author on reasonable request and with permission of Sun Yat-sen University Cancer Center (Guangzhou, China).

Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The experiments comply with the current laws of China.

Author contribution statement

Study conception and design was performed by Zhongyu Yuan and Xinyue Wang. Acquisition of data was performed by Xinyue Wang, Zhangzan Huang, and Wei Shi. Analysis and interpretation of data was performed by Xinyue Wang and Xiwen Bi. Drafting of manuscript was performed by Xinyue Wang and Xiwen Bi. Critical revision was performed by Zhongyu Yuan, Jiajia Huang, Xiwen Bi, and Wen Xia. Final approval of the version to be submitted was performed by Xinyue Wang, Xiwen Bi, Zhangzan Huang, Jiajia Huang, Wen Xia, Wei Shi, and Zhongyu Yuan.

Acknowledgments

The authors would like to acknowledge technical support in immunohistochemical procedures to Jiabin Lu, and data management as well as quality control to Yongyi Zhong.

References

  • Agoff SN, Swanson PE, Linden H, Hawes SE & Lawton TJ 2003 Androgen receptor expression in estrogen receptor-negative breast cancer. Immunohistochemical, clinical, and prognostic associations. American Journal of Clinical Pathology 725731. (https://doi.org/10.1309/42F00D0DJD0J5EDT)

    • Search Google Scholar
    • Export Citation
  • Aleskandarany MA, Abduljabbar R, Ashankyty I, Elmouna A, Jerjees D, Ali S, Buluwela L, Diez-Rodriguez M, Caldas C, Green AR, et al.2016 Prognostic significance of androgen receptor expression in invasive breast cancer: transcriptomic and protein expression analysis. Breast Cancer Research and Treatment 215227. (https://doi.org/10.1007/s10549-016-3934-5)

    • Search Google Scholar
    • Export Citation
  • Arteaga CL, Sliwkowski MX, Osborne CK, Perez EA, Puglisi F & Gianni L 2011 Treatment of HER2-positive breast cancer: current status and future perspectives. Nature Reviews: Clinical Oncology 1632. (https://doi.org/10.1038/nrclinonc.2011.177)

    • Search Google Scholar
    • Export Citation
  • Asano Y, Kashiwagi S, Goto W, Tanaka S, Morisaki T, Takashima T, Noda S, Onoda N, Ohsawa M, Hirakawa K, et al.2017 Expression and clinical significance of androgen receptor in triple-negative breast cancer. Cancers 9 4. (https://doi.org/10.3390/cancers9010004)

    • Search Google Scholar
    • Export Citation
  • Barton VN, D’Amato NC, Gordon MA, Lind HT, Spoelstra NS, Babbs BL, Heinz RE, Elias A, Jedlicka P, Jacobsen BM, et al.2015 Multiple molecular subtypes of triple-negative breast cancer critically rely on androgen receptor and respond to enzalutamide in vivo. Molecular Cancer Therapeutics 769778. (https://doi.org/10.1158/1535-7163.MCT-14-0926)

    • Search Google Scholar
    • Export Citation
  • Basile D, Cinausero M, Iacono D, Pelizzari G, Bonotto M, Vitale MG, Gerratana L & Puglisi F 2017 Androgen receptor in estrogen receptor positive breast cancer: beyond expression. Cancer Treatment Reviews 1522. (https://doi.org/10.1016/j.ctrv.2017.09.006)

    • Search Google Scholar
    • Export Citation
  • Bozovic-Spasojevic I, Zardavas D, Brohee S, Ameye L, Fumagalli D, Ades F, de Azambuja E, Bareche Y, Piccart M, Paesmans M, et al.2017 The prognostic role of androgen receptor in patients with early-stage breast cancer: a meta-analysis of clinical and gene expression data. Clinical Cancer Research 27022712. (https://doi.org/10.1158/1078-0432.CCR-16-0979)

    • Search Google Scholar
    • Export Citation
  • Carey LA, Perou CM, Livasy CA, Dressler LG, Cowan D, Conway K, Karaca G, Troester MA, Tse CK, Edmiston S, et al.2006 Race, breast cancer subtypes, and survival in the Carolina Breast Cancer Study. JAMA 24922502. (https://doi.org/10.1001/jama.295.21.2492)

    • Search Google Scholar
    • Export Citation
  • Chia K, O’Brien M, Brown M & Lim E 2015 Targeting the androgen receptor in breast cancer. Current Oncology Reports 4. (https://doi.org/10.1007/s11912-014-0427-8)

    • Search Google Scholar
    • Export Citation
  • Collins LC, Cole KS, Marotti JD, Hu R, Schnitt SJ & Tamimi RM 2011 Androgen receptor expression in breast cancer in relation to molecular phenotype: results from the Nurses’ Health Study. Modern Pathology 924931. (https://doi.org/10.1038/modpathol.2011.54)

    • Search Google Scholar
    • Export Citation
  • Elebro K, Bendahl PO, Jernstrom H & Borgquist S 2017 Androgen receptor expression and breast cancer mortality in a population-based prospective cohort. Breast Cancer Research and Treatment 645657. (https://doi.org/10.1007/s10549-017-4343-0)

    • Search Google Scholar
    • Export Citation
  • Giuliano AE, Connolly JL, Edge SB, Mittendorf EA, Rugo HS, Solin LJ, Weaver DL, Winchester DJ & Hortobagyi GN 2017 Breast cancer-major changes in the American Joint Committee on cancer eighth edition cancer staging manual. CA: A Cancer Journal for Clinicians 290303. (https://doi.org/10.3322/caac.21393)

    • Search Google Scholar
    • Export Citation
  • Gordon MA, D’Amato NC, Gu H, Babbs B, Wulfkuhle J, Petricoin EF, Gallagher I, Dong T, Torkko K, Liu B, et al.2017 Synergy between androgen receptor antagonism and inhibition of mTOR and HER2 in breast cancer. Molecular Cancer Therapeutics 13891400. (https://doi.org/10.1158/1535-7163.MCT-17-0111)

    • Search Google Scholar
    • Export Citation
  • Gucalp A, Tolaney S, Isakoff SJ, Ingle JN, Liu MC, Carey LA, Blackwell K, Rugo H, Nabell L, Forero A, et al.2013 Phase II trial of bicalutamide in patients with androgen receptor-positive, estrogen receptor-negative metastatic breast cancer. Clinical Cancer Research 55055512. (https://doi.org/10.1158/1078-0432.CCR-12-3327)

    • Search Google Scholar
    • Export Citation
  • Hilborn E, Gacic J, Fornander T, Nordenskjold B, Stal O & Jansson A 2016 Androgen receptor expression predicts beneficial tamoxifen response in oestrogen receptor-alpha-negative breast cancer. British Journal of Cancer 248255. (https://doi.org/10.1038/bjc.2015.464)

    • Search Google Scholar
    • Export Citation
  • Honma N, Horii R, Iwase T, Saji S, Younes M, Ito Y & Akiyama F 2012 Clinical importance of androgen receptor in breast cancer patients treated with adjuvant tamoxifen monotherapy. Breast Cancer 20 323330. (https://doi.org/10.1007/s12282-012-0337-2)

    • Search Google Scholar
    • Export Citation
  • Kravchenko J, Akushevich I, Seewaldt VL, Abernethy AP & Lyerly HK 2011 Breast cancer as heterogeneous disease: contributing factors and carcinogenesis mechanisms. Breast Cancer Research and Treatment 483493. (https://doi.org/10.1007/s10549-011-1347-z)

    • Search Google Scholar
    • Export Citation
  • Lea OA, Kvinnsland S & Thorsen T 1989 Improved measurement of androgen receptors in human breast cancer. Cancer Research 71627167.

  • Loibl S, Muller BM, von Minckwitz G, Schwabe M, Roller M, Darb-Esfahani S, Ataseven B, du Bois A, Fissler-Eckhoff A, Gerber B, et al.2011 Androgen receptor expression in primary breast cancer and its predictive and prognostic value in patients treated with neoadjuvant chemotherapy. Breast Cancer Research and Treatment 477487. (https://doi.org/10.1007/s10549-011-1715-8)

    • Search Google Scholar
    • Export Citation
  • McNamara KM, Moore NL, Hickey TE, Sasano H & Tilley WD 2014 Complexities of androgen receptor signalling in breast cancer. Endocrine-Related Cancer T161T181. (https://doi.org/10.1530/ERC-14-0243)

    • Search Google Scholar
    • Export Citation
  • McShane LM, Altman DG, Sauerbrei W, Taube SE, Gion M, Clark GM & Statistics Subcommittee of the NCI-EORTC Working Group on Cancer Diagnostics 2005 REporting recommendations for tumour MARKer prognostic studies (REMARK). British Journal of Cancer 387391. (https://doi.org/10.1038/sj.bjc.6602678)

    • Search Google Scholar
    • Export Citation
  • Moinfar F, Okcu M, Tsybrovskyy O, Regitnig P, Lax SF, Weybora W, Ratschek M, Tavassoli FA & Denk H 2003 Androgen receptors frequently are expressed in breast carcinomas: potential relevance to new therapeutic strategies. Cancer 703711. (https://doi.org/10.1002/cncr.11532)

    • Search Google Scholar
    • Export Citation
  • NCCN 2018 NCCN clinical practice guidelines in oncology: breast cancer. Plymouth Meeting, PA, USA: National Comprehensive Cancer Network. (available at: https://www.nccn.org/professionals/physician_gls/default.aspx)

    • Search Google Scholar
    • Export Citation
  • Ni M, Chen Y, Lim E, Wimberly H, Bailey ST, Imai Y, Rimm DL, Liu XS & Brown M 2011 Targeting androgen receptor in estrogen receptor-negative breast cancer. Cancer Cell 119131. (https://doi.org/10.1016/j.ccr.2011.05.026)

    • Search Google Scholar
    • Export Citation
  • Park S, Koo J, Park HS, Kim JH, Choi SY, Lee JH, Park BW & Lee KS 2010 Expression of androgen receptors in primary breast cancer. Annals of Oncology 488492. (https://doi.org/10.1093/annonc/mdp510)

    • Search Google Scholar
    • Export Citation
  • Peters AA, Buchanan G, Ricciardelli C, Bianco-Miotto T, Centenera MM, Harris JM, Jindal S, Segara D, Jia L, Moore NL, et al.2009 Androgen receptor inhibits estrogen receptor-alpha activity and is prognostic in breast cancer. Cancer Research 61316140. (https://doi.org/10.1158/0008-5472.CAN-09-0452)

    • Search Google Scholar
    • Export Citation
  • Pusztai L, Viale G, Kelly CM & Hudis CA 2010 Estrogen and HER-2 receptor discordance between primary breast cancer and metastasis. Oncologist 11641168. (https://doi.org/10.1634/theoncologist.2010-0059)

    • Search Google Scholar
    • Export Citation
  • Qu Q, Mao Y, Fei XC & Shen KW 2013 The impact of androgen receptor expression on breast cancer survival: a retrospective study and meta-analysis. PLoS ONE e82650. (https://doi.org/10.1371/journal.pone.0082650)

    • Search Google Scholar
    • Export Citation
  • Rangel N, Rondon-Lagos M, Annaratone L, Osella-Abate S, Metovic J, Mano MP, Bertero L, Cassoni P, Sapino A & Castellano I 2018 The role of the AR/ER ratio in ER-positive breast cancer patients. Endocrine-Related Cancer 163172. (https://doi.org/10.1530/ERC-17-0417)

    • Search Google Scholar
    • Export Citation
  • Romond EH, Perez EA, Bryant J, Suman VJ, Geyer CE Jr, Davidson NE, Tan-Chiu E, Martino S, Paik S, Kaufman PA, et al.2005 Trastuzumab plus adjuvant chemotherapy for operable HER2-positive breast cancer. New England Journal of Medicine 16731684. (https://doi.org/10.1056/NEJMoa052122)

    • Search Google Scholar
    • Export Citation
  • Slamon DJ, Leyland-Jones B, Shak S, Fuchs H, Paton V, Bajamonde A, Fleming T, Eiermann W, Wolter J, Pegram M, et al.2001 Use of chemotherapy plus a monoclonal antibody against HER2 for metastatic breast cancer that overexpresses HER2. New England Journal of Medicine 783792. (https://doi.org/10.1056/NEJM200103153441101)

    • Search Google Scholar
    • Export Citation
  • Stern HM 2012 Improving treatment of HER2-positive cancers: opportunities and challenges. Science Translational Medicine 127rv2. (https://doi.org/10.1126/scitranslmed.3001539)

    • Search Google Scholar
    • Export Citation
  • Vera-Badillo FE, Templeton AJ, de Gouveia P, Diaz-Padilla I, Bedard PL, Al-Mubarak M, Seruga B, Tannock IF, Ocana A & Amir E 2014 Androgen receptor expression and outcomes in early breast cancer: a systematic review and meta-analysis. Journal of the National Cancer Institute djt319. (https://doi.org/10.1093/jnci/djt319)

    • Search Google Scholar
    • Export Citation
  • Wolff AC, Hammond ME, Hicks DG, Dowsett M, McShane LM, Allison KH, Allred DC, Bartlett JM, Bilous M, Fitzgibbons P, et al.2013 Recommendations for human epidermal growth factor receptor 2 testing in breast cancer: American Society of Clinical Oncology/College of American Pathologists clinical practice guideline update. Journal of Clinical Oncology 39974013. (https://doi.org/10.1200/JCO.2013.50.9984)

    • Search Google Scholar
    • Export Citation

 

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  • View in gallery

    Study flow diagram of the study.

  • View in gallery

    Representative images of AR staining in three cases. AR-negative (A, 100× magnification; B, 200× magnification), AR-positive with nuclear staining of 10% (C, 100× magnification; D, 200× magnification), and AR-positive with nuclear staining >90% (E, 100× magnification; F, 200× magnification). AR, androgen receptor. A full color version of this figure is available at https://doi.org/10.1530/ERC-19-0315.

  • View in gallery

    Distribution and discordance rate of AR expression level. (A) Distribution of AR status on primary tumor (red, 169 cases), metastatic lesions (blue, 135 cases), and both sites (green, 24 cases) in 304 patients with HER2-enriched MBC. (B) The percentage change of AR staining level from primary tumor to paired metastatic lesions for 24 cases. AR, androgen receptor. A full color version of this figure is available at https://doi.org/10.1530/ERC-19-0315.

  • View in gallery

    Progression-free survival (A) and overall survival (B) in 304 patients with HER2-enriched MBC were calculated using the Kaplan–Meier method, respectively. The log-rank test was used to compare the differences between the study arms. Cut-off at 10% for AR-positivity. AR, androgen receptor. A full color version of this figure is available at https://doi.org/10.1530/ERC-19-0315.

  • View in gallery

    Progression-free survival (A) and overall survival (B) were calculated using the Kaplan–Meier method for patients who received first-line Trastuzumab treatment, respectively. The log-rank test was used to compare the differences between the study arms. Cut-off at 10% for AR-positivity. AR, androgen receptor. A full color version of this figure is available at https://doi.org/10.1530/ERC-19-0315.

  • Agoff SN, Swanson PE, Linden H, Hawes SE & Lawton TJ 2003 Androgen receptor expression in estrogen receptor-negative breast cancer. Immunohistochemical, clinical, and prognostic associations. American Journal of Clinical Pathology 725731. (https://doi.org/10.1309/42F00D0DJD0J5EDT)

    • Search Google Scholar
    • Export Citation
  • Aleskandarany MA, Abduljabbar R, Ashankyty I, Elmouna A, Jerjees D, Ali S, Buluwela L, Diez-Rodriguez M, Caldas C, Green AR, et al.2016 Prognostic significance of androgen receptor expression in invasive breast cancer: transcriptomic and protein expression analysis. Breast Cancer Research and Treatment 215227. (https://doi.org/10.1007/s10549-016-3934-5)

    • Search Google Scholar
    • Export Citation
  • Arteaga CL, Sliwkowski MX, Osborne CK, Perez EA, Puglisi F & Gianni L 2011 Treatment of HER2-positive breast cancer: current status and future perspectives. Nature Reviews: Clinical Oncology 1632. (https://doi.org/10.1038/nrclinonc.2011.177)

    • Search Google Scholar
    • Export Citation
  • Asano Y, Kashiwagi S, Goto W, Tanaka S, Morisaki T, Takashima T, Noda S, Onoda N, Ohsawa M, Hirakawa K, et al.2017 Expression and clinical significance of androgen receptor in triple-negative breast cancer. Cancers 9 4. (https://doi.org/10.3390/cancers9010004)

    • Search Google Scholar
    • Export Citation
  • Barton VN, D’Amato NC, Gordon MA, Lind HT, Spoelstra NS, Babbs BL, Heinz RE, Elias A, Jedlicka P, Jacobsen BM, et al.2015 Multiple molecular subtypes of triple-negative breast cancer critically rely on androgen receptor and respond to enzalutamide in vivo. Molecular Cancer Therapeutics 769778. (https://doi.org/10.1158/1535-7163.MCT-14-0926)

    • Search Google Scholar
    • Export Citation
  • Basile D, Cinausero M, Iacono D, Pelizzari G, Bonotto M, Vitale MG, Gerratana L & Puglisi F 2017 Androgen receptor in estrogen receptor positive breast cancer: beyond expression. Cancer Treatment Reviews 1522. (https://doi.org/10.1016/j.ctrv.2017.09.006)

    • Search Google Scholar
    • Export Citation
  • Bozovic-Spasojevic I, Zardavas D, Brohee S, Ameye L, Fumagalli D, Ades F, de Azambuja E, Bareche Y, Piccart M, Paesmans M, et al.2017 The prognostic role of androgen receptor in patients with early-stage breast cancer: a meta-analysis of clinical and gene expression data. Clinical Cancer Research 27022712. (https://doi.org/10.1158/1078-0432.CCR-16-0979)

    • Search Google Scholar
    • Export Citation
  • Carey LA, Perou CM, Livasy CA, Dressler LG, Cowan D, Conway K, Karaca G, Troester MA, Tse CK, Edmiston S, et al.2006 Race, breast cancer subtypes, and survival in the Carolina Breast Cancer Study. JAMA 24922502. (https://doi.org/10.1001/jama.295.21.2492)

    • Search Google Scholar
    • Export Citation
  • Chia K, O’Brien M, Brown M & Lim E 2015 Targeting the androgen receptor in breast cancer. Current Oncology Reports 4. (https://doi.org/10.1007/s11912-014-0427-8)

    • Search Google Scholar
    • Export Citation
  • Collins LC, Cole KS, Marotti JD, Hu R, Schnitt SJ & Tamimi RM 2011 Androgen receptor expression in breast cancer in relation to molecular phenotype: results from the Nurses’ Health Study. Modern Pathology 924931. (https://doi.org/10.1038/modpathol.2011.54)

    • Search Google Scholar
    • Export Citation
  • Elebro K, Bendahl PO, Jernstrom H & Borgquist S 2017 Androgen receptor expression and breast cancer mortality in a population-based prospective cohort. Breast Cancer Research and Treatment 645657. (https://doi.org/10.1007/s10549-017-4343-0)

    • Search Google Scholar
    • Export Citation
  • Giuliano AE, Connolly JL, Edge SB, Mittendorf EA, Rugo HS, Solin LJ, Weaver DL, Winchester DJ & Hortobagyi GN 2017 Breast cancer-major changes in the American Joint Committee on cancer eighth edition cancer staging manual. CA: A Cancer Journal for Clinicians 290303. (https://doi.org/10.3322/caac.21393)

    • Search Google Scholar
    • Export Citation
  • Gordon MA, D’Amato NC, Gu H, Babbs B, Wulfkuhle J, Petricoin EF, Gallagher I, Dong T, Torkko K, Liu B, et al.2017 Synergy between androgen receptor antagonism and inhibition of mTOR and HER2 in breast cancer. Molecular Cancer Therapeutics 13891400. (https://doi.org/10.1158/1535-7163.MCT-17-0111)

    • Search Google Scholar
    • Export Citation
  • Gucalp A, Tolaney S, Isakoff SJ, Ingle JN, Liu MC, Carey LA, Blackwell K, Rugo H, Nabell L, Forero A, et al.2013 Phase II trial of bicalutamide in patients with androgen receptor-positive, estrogen receptor-negative metastatic breast cancer. Clinical Cancer Research 55055512. (https://doi.org/10.1158/1078-0432.CCR-12-3327)

    • Search Google Scholar
    • Export Citation
  • Hilborn E, Gacic J, Fornander T, Nordenskjold B, Stal O & Jansson A 2016 Androgen receptor expression predicts beneficial tamoxifen response in oestrogen receptor-alpha-negative breast cancer. British Journal of Cancer 248255. (https://doi.org/10.1038/bjc.2015.464)

    • Search Google Scholar
    • Export Citation
  • Honma N, Horii R, Iwase T, Saji S, Younes M, Ito Y & Akiyama F 2012 Clinical importance of androgen receptor in breast cancer patients treated with adjuvant tamoxifen monotherapy. Breast Cancer 20 323330. (https://doi.org/10.1007/s12282-012-0337-2)

    • Search Google Scholar
    • Export Citation
  • Kravchenko J, Akushevich I, Seewaldt VL, Abernethy AP & Lyerly HK 2011 Breast cancer as heterogeneous disease: contributing factors and carcinogenesis mechanisms. Breast Cancer Research and Treatment 483493. (https://doi.org/10.1007/s10549-011-1347-z)

    • Search Google Scholar
    • Export Citation
  • Lea OA, Kvinnsland S & Thorsen T 1989 Improved measurement of androgen receptors in human breast cancer. Cancer Research 71627167.

  • Loibl S, Muller BM, von Minckwitz G, Schwabe M, Roller M, Darb-Esfahani S, Ataseven B, du Bois A, Fissler-Eckhoff A, Gerber B, et al.2011 Androgen receptor expression in primary breast cancer and its predictive and prognostic value in patients treated with neoadjuvant chemotherapy. Breast Cancer Research and Treatment 477487. (https://doi.org/10.1007/s10549-011-1715-8)

    • Search Google Scholar
    • Export Citation
  • McNamara KM, Moore NL, Hickey TE, Sasano H & Tilley WD 2014 Complexities of androgen receptor signalling in breast cancer. Endocrine-Related Cancer T161T181. (https://doi.org/10.1530/ERC-14-0243)

    • Search Google Scholar
    • Export Citation
  • McShane LM, Altman DG, Sauerbrei W, Taube SE, Gion M, Clark GM & Statistics Subcommittee of the NCI-EORTC Working Group on Cancer Diagnostics 2005 REporting recommendations for tumour MARKer prognostic studies (REMARK). British Journal of Cancer 387391. (https://doi.org/10.1038/sj.bjc.6602678)

    • Search Google Scholar
    • Export Citation
  • Moinfar F, Okcu M, Tsybrovskyy O, Regitnig P, Lax SF, Weybora W, Ratschek M, Tavassoli FA & Denk H 2003 Androgen receptors frequently are expressed in breast carcinomas: potential relevance to new therapeutic strategies. Cancer 703711. (https://doi.org/10.1002/cncr.11532)

    • Search Google Scholar
    • Export Citation
  • NCCN 2018 NCCN clinical practice guidelines in oncology: breast cancer. Plymouth Meeting, PA, USA: National Comprehensive Cancer Network. (available at: https://www.nccn.org/professionals/physician_gls/default.aspx)

    • Search Google Scholar
    • Export Citation
  • Ni M, Chen Y, Lim E, Wimberly H, Bailey ST, Imai Y, Rimm DL, Liu XS & Brown M 2011 Targeting androgen receptor in estrogen receptor-negative breast cancer. Cancer Cell 119131. (https://doi.org/10.1016/j.ccr.2011.05.026)

    • Search Google Scholar
    • Export Citation
  • Park S, Koo J, Park HS, Kim JH, Choi SY, Lee JH, Park BW & Lee KS 2010 Expression of androgen receptors in primary breast cancer. Annals of Oncology 488492. (https://doi.org/10.1093/annonc/mdp510)

    • Search Google Scholar
    • Export Citation
  • Peters AA, Buchanan G, Ricciardelli C, Bianco-Miotto T, Centenera MM, Harris JM, Jindal S, Segara D, Jia L, Moore NL, et al.2009 Androgen receptor inhibits estrogen receptor-alpha activity and is prognostic in breast cancer. Cancer Research 61316140. (https://doi.org/10.1158/0008-5472.CAN-09-0452)

    • Search Google Scholar
    • Export Citation
  • Pusztai L, Viale G, Kelly CM & Hudis CA 2010 Estrogen and HER-2 receptor discordance between primary breast cancer and metastasis. Oncologist 11641168. (https://doi.org/10.1634/theoncologist.2010-0059)

    • Search Google Scholar
    • Export Citation
  • Qu Q, Mao Y, Fei XC & Shen KW 2013 The impact of androgen receptor expression on breast cancer survival: a retrospective study and meta-analysis. PLoS ONE e82650. (https://doi.org/10.1371/journal.pone.0082650)

    • Search Google Scholar
    • Export Citation
  • Rangel N, Rondon-Lagos M, Annaratone L, Osella-Abate S, Metovic J, Mano MP, Bertero L, Cassoni P, Sapino A & Castellano I 2018 The role of the AR/ER ratio in ER-positive breast cancer patients. Endocrine-Related Cancer 163172. (https://doi.org/10.1530/ERC-17-0417)

    • Search Google Scholar
    • Export Citation
  • Romond EH, Perez EA, Bryant J, Suman VJ, Geyer CE Jr, Davidson NE, Tan-Chiu E, Martino S, Paik S, Kaufman PA, et al.2005 Trastuzumab plus adjuvant chemotherapy for operable HER2-positive breast cancer. New England Journal of Medicine 16731684. (https://doi.org/10.1056/NEJMoa052122)

    • Search Google Scholar
    • Export Citation
  • Slamon DJ, Leyland-Jones B, Shak S, Fuchs H, Paton V, Bajamonde A, Fleming T, Eiermann W, Wolter J, Pegram M, et al.2001 Use of chemotherapy plus a monoclonal antibody against HER2 for metastatic breast cancer that overexpresses HER2. New England Journal of Medicine 783792. (https://doi.org/10.1056/NEJM200103153441101)

    • Search Google Scholar
    • Export Citation
  • Stern HM 2012 Improving treatment of HER2-positive cancers: opportunities and challenges. Science Translational Medicine 127rv2. (https://doi.org/10.1126/scitranslmed.3001539)

    • Search Google Scholar
    • Export Citation
  • Vera-Badillo FE, Templeton AJ, de Gouveia P, Diaz-Padilla I, Bedard PL, Al-Mubarak M, Seruga B, Tannock IF, Ocana A & Amir E 2014 Androgen receptor expression and outcomes in early breast cancer: a systematic review and meta-analysis. Journal of the National Cancer Institute djt319. (https://doi.org/10.1093/jnci/djt319)

    • Search Google Scholar
    • Export Citation
  • Wolff AC, Hammond ME, Hicks DG, Dowsett M, McShane LM, Allison KH, Allred DC, Bartlett JM, Bilous M, Fitzgibbons P, et al.2013 Recommendations for human epidermal growth factor receptor 2 testing in breast cancer: American Society of Clinical Oncology/College of American Pathologists clinical practice guideline update. Journal of Clinical Oncology 39974013. (https://doi.org/10.1200/JCO.2013.50.9984)

    • Search Google Scholar
    • Export Citation