Neuroendocrine differentiation in usual-type prostatic adenocarcinoma: Molecular characterization and clinical significance

Abstract

Background: Small cell neuroendocrine (NE) carcinomas of the prostate classically lose androgen receptor (AR) expression, may harbor loss of the RB1, TP53, and PTEN tumor suppressor genes, and are associated with a poor prognosis. However usual-type adenocarcinomas may also contain areas of NE differentiation, and in this context the molecular features and biological significance are less certain.

Methods: We examined the molecular phenotype and oncologic outcomes of primary prostate adenocarcinomas with ≥5% NE differentiation (≥5% chromogranin A-positive NE cells in any given tumor spot on tissue microarray) using three independent study sets: a set of tumors with paneth cell-like NE differentiation (n = 26), a retrospective case-cohort of intermediate- and high-risk patients enriched for adverse outcomes (n = 267), and primary tumors from a retrospective series of men with eventual castration-resistant metastatic prostate cancer (CRPC) treated with abiraterone or enzalutamide (n = 55).

Results: Benign NE cells expressed significantly lower quantified AR levels compared with paired benign luminal cells (P < .001). Similarly, paneth-like NE carcinoma cells or carcinoma cells expressing chromogranin A expressed significantly lower quantified AR levels than paired non-NE carcinoma cells (P < .001). Quantified ERG protein expression, was also lower in chromogranin A-labeled adenocarcinoma cells compared with unlabeled cells (P < .001) and tumors with NE differentiation showed lower gene expression scores for AR activity compared with those without. Despite evidence of lower AR signaling, adenocarcinomas with NE differentiation did not differ by prevalence of TP53 missense mutations, or PTEN or RB1 loss, compared with those without NE differentiation. Finally, NE differentiation was not associated with time to metastasis in intermediate- and high-risk patients (P = .6 on multivariate analysis), nor with progression-free survival in patients with CRPC treated with abiraterone or enzalutamide (P = .9).

Conclusion: NE differentiation in usual-type primary prostate adenocarcinoma is a molecularly and clinically distinct form of lineage plasticity from that occurring in small cell NE carcinoma.

Keywords: androgen receptor; neuroendocrine differentiation; paneth cells; prostate adenocarcinoma.

Figure 1:. AR expression in benign NE cells.

(A) Representative AR and chromogranin A immunostaining in formalin fixed paraffin embedded benign prostate glands. The histologic sections were subjected to indirect immunofluorescence with anti-AR (red) and anti-chromogranin (green) antibodies to detect neuroendocrine cells and quantify AR expression. Images reduced from 630X. (B) Absolute androgen receptor (AR) expression level comparison between benign luminal and benign neuroendocrine cells. p-value by paired T-test.

Figure 2:. AR expression in Paneth cell-like carcinoma cells.

(A) Representative H&E, AR and INSM1 immunostaining (Case 3) in formalin fixed and paraffin embedded primary prostate tumors with Paneth cell-like differentiation. INSM1 labeling clearly identified Paneth cell-like tumor cells by immunohistochemical labeling and AR expression in an adjacent section showed decreased AR expression when compared to non-NE carcinoma cells. Case 4 shows representative H&E, with dual immunofluorescence for AR (red) and INSM1 (green). Images reduced from 200X (IHC) and 630X (Immunofluorescence). (B) Absolute androgen receptor (AR) expression level comparison between Paneth-like cells and prostate adenocarcinoma (PCa) cells. p-value by paired T-test.

Figure 3:. AR expression in NE carcinoma cells.

(A) Representative H&E with AR (red) and chromogranin A (green) dual immunofluorescence in formalin fixed and paraffin embedded usual-type primary prostate tumors with significant NE differentiation. Images reduced from 630X. (B) Absolute androgen receptor (AR) expression level comparison between neuroendocrine (NE) cells and prostate adenocarcinoma (PCa) cells. p-value by paired T-test.

Figure 4:. ERG expression in NE carcinoma cells.

(A) Representative ERG (red) and chromogranin A (green) immunofluorescence in formalin fixed and paraffin embedded usual-type primary prostate tumors with significant NE differentiation. (B) Absolute ERG expression level comparison between neuroendocrine (NE) cells and prostate adenocarcinoma (PCa) cells. p-value by paired T-test.

Figure 5:. NE and androgen receptor activity gene expression in carcinomas with and without significant NE differentiation.

Comparison of tumors with and without significant neuroendocrine (NE) differentiation (as defined by a 5% cutoff for chromogranin A staining) in Intermediate/High Risk cohort (21) for (A) CHGA gene expression, (B) NE prostate cancer signature activity (37), (C) AR activity score (AR-A) (38, 39) and (D) AR activity (37). p-values by Wilcoxon test.