Neuroendocrine neoplasia is described in almost every tissue, either in the pure endocrine organs, the nerve structures or in the so-called diffuse neuroendocrine system. The current nomenclature contains time-honored, widely accepted definitions; however, it is different according to anatomical sites. Diverse definitions may generate confusion and non-standard patient management. The International Agency for Research on Cancer – World Health Organization (IARC-WHO) proposed a framework for universal classification of neuroendocrine neoplasia. Evidence indicates that neuroendocrine cancer is composed by cells with a distinctive phenotype characterized by the expression of general and specific neuroendocrine markers. The neuroendocrine phenotype is indicated as descriptor of a unique cancer category, now recommended for all organs as neuroendocrine neoplasm. Evidence indicates that neuroendocrine neoplasia may be well or poorly differentiated, with diverse incidence and prevalence in different organs. It is proposed that the well-differentiated neoplasm is universally defined as neuroendocrine tumor (NET) and the poorly differentiated as neoplasm neuroendocrine carcinoma (NEC). Evidence indicates that a cancer grading tool based on a proliferation measure by mitotic count, Ki67 % and/or necrosis assessment is useful to predict NET patient behavior. It is proposed to utilize this tool for grading NET universally, with site-specific cut-offs to be defined. It is also acknowledged that significant biological site-specific differences exist. It is recommended that current pathology reports contain this classification together with the current traditional classifiers. This IARC-WHO common classification framework for neuroendocrine neoplasm aims at uniformizing nomenclature toward different organs and at fostering the definition of a similar site-specific gene signature.

Among alternative therapeutic strategies in clinically aggressive neuroendocrine tumors (NETs) of the lung, promising results have been obtained in experimental clinical trials with mammalian target of rapamycin (mTOR) inhibitors, though in the absence of a proven mTOR signaling activation status. This study analyzed the expression of phosphorylated mTOR (p-mTOR) and its major targets, the ribosomal p70S6-kinase (S6K) and the eukaryotic initiation factor 4E-binding protein 1 (4EBP1) in a large series of 218 surgically resected, malignant lung NETs, including 24 metastasizing typical carcinoids, 73 atypical carcinoids, 60 large cell neuroendocrine carcinomas (LCNECs), and 61 small cell carcinomas (SCLCs). By immunohistochemistry, low-to-intermediate-grade tumors as compared with high-grade tumors showed higher levels of p-mTOR and phosphorylated S6K (p-S6K) (P<0.001), at variance with phosphorylated 4EBP1 (p-4EBP1), which was mainly expressed in LCNECs and SCLCs (P<0.001). The activated status of mTOR pathway was proved by the strong correlation of p-mTOR with p-S6K and somatostatin receptor(s). Western blot analysis of NET tumor samples confirmed such findings, and differential sensitivity to mTOR inhibition according to mTOR pathway activation characteristics was determined in two lung carcinoid cell lines in vitro. None of the investigated molecules had an impact on survival. However, in low-grade tumors, low p-mTOR expression correlated with lymph node metastases (P=0.016), recurrent disease, and survival (P=0.005). In conclusion, these data demonstrate a differential mTOR activation status in the spectrum of pulmonary NETs, possibly suggesting that mTOR pathway profiling might play a predictive role in candidate patients for mTOR-targeted therapies.

Mixed adenoneuroendocrine carcinomas (MANECs) are composed of a poorly differentiated neuroendocrine carcinoma (NEC) and a non-neuroendocrine (non-NEC) neoplastic epithelial component, each representing at least 30% of the tumor. At present, prognostic factors for MANECs remain largely unexplored. We investigated the clinical-pathologic features of a large multicenter series of digestive system MANECs. Surgical specimens of 200 MANEC candidates were centrally reviewed; diagnosis was confirmed in 160 cases. While morphology, proliferation (mitotic count (MC), Ki67 index) and immunophenotype (p53, SSTR2a, beta-Catenin, Bcl-2, p16, Rb1, ALDH, mismatch repair proteins and CD117) were investigated separately in both components, genomic (TP53, KRAS, BRAF) alterations were searched for on the entire tumor. Data were correlated with overall survival (OS). MANEC sites were: 92 colorectal, 44 gastroesophageal and 24 pancreatobiliary. Median OS was 13.2 months. After adjustment for primary site, Ki67 index of the NEC component (but not of the non-NEC component) was the most powerful prognostic marker. At multivariable analysis, patients with Ki67 ≥ 55% had an 8-fold risk of death (hazard ratio (HR) 7.83; 95% confidence interval (CI) 4.17–14.7; P < 0.0001) and a median OS of 12.2 months compared to those with Ki67 < 55% (median OS 40.5 months). MC (HR 1.51; 95% CI 1.03–2.20, P = 0.04) was a weaker prognostic index. Colorectal primary site (HR 1.60; 95% CI 1.11–2.32; P = 0.01) was significantly associated with poorer survival. No single immunomarker, in either component, was statistically significant. This retrospective analysis of a large series of digestive system MANECs, showed that the NEC component, particularly its Ki67 index, was the main prognostic driver.