Purpose: The prevalence and features of treatment-emergent small-cell neuroendocrine prostate cancer (t-SCNC) are not well characterized in the era of modern androgen receptor (AR)–targeting therapy. We sought to characterize the clinical and genomic features of t-SCNC in a multi-institutional prospective study. Methods: Patients with progressive, metastatic castration-resistant prostate cancer (mCRPC) underwent metastatic tumor biopsy and were followed for survival. Metastatic biopsy specimens underwent independent, blinded pathology review along with RNA/DNA sequencing. Results: A total of 202 consecutive patients were enrolled. One hundred forty-eight (73%) had prior disease progression on abiraterone and/or enzalutamide. The biopsy evaluable rate was 79%. The overall incidence of t-SCNC detection was 17%. AR amplification and protein expression were present in 67% and 75%, respectively, of t-SCNC biopsy specimens. t-SCNC was detected at similar proportions in bone, node, and visceral organ biopsy specimens. Genomic alterations in the DNA repair pathway were nearly mutually exclusive with t-SCNC differentiation ( P = .035). Detection of t-SCNC was associated with shortened overall survival among patients with prior AR-targeting therapy for mCRPC (hazard ratio, 2.02; 95% CI, 1.07 to 3.82). Unsupervised hierarchical clustering of the transcriptome identified a small-cell–like cluster that further enriched for adverse survival outcomes (hazard ratio, 3.00; 95% CI, 1.25 to 7.19). A t-SCNC transcriptional signature was developed and validated in multiple external data sets with > 90% accuracy. Multiple transcriptional regulators of t-SCNC were identified, including the pancreatic neuroendocrine marker PDX1. Conclusion: t-SCNC is present in nearly one fifth of patients with mCRPC and is associated with shortened survival. The near-mutual exclusivity with DNA repair alterations suggests t-SCNC may be a distinct subset of mCRPC. Transcriptional profiling facilitates the identification of t-SCNC and novel therapeutic targets.

Neuroendocrine prostate cancer (NEPC) encompasses various clinical contexts, ranging from the de novo presentation of small cell prostatic carcinoma to a treatment-emergent transformed phenotype that arises from typical adenocarcinoma of the prostate. The development of resistance to potent androgen receptor signaling inhibition may be associated with the emergence of aggressive phenotype, advanced castration-resistant NEPC. Clinically, small cell prostate cancer and NEPC are often manifested by the presence of visceral or large soft tissue metastatic disease, a disproportionately low serum prostate-specific antigen level relative to the overall burden of disease, and a limited response to targeting of the androgen signaling axis. These tumors are often characterized by loss of androgen receptor expression, loss of retinoblastoma tumor suppressor copy number or expression, amplification of Aurora kinase A and N-Myc, and activation of the PI3K pathway. However, a consensus phenotype-genotype definition of NEPC has yet to emerge, and molecularly based biomarkers are needed to expand on traditional morphologic and immunohistochemical markers of NEPC to fully define the spectrum of this aggressive, androgen receptor-independent disease. Emerging studies implicate a shared clonal origin with prostatic adenocarcinoma in many cases, with the adaptive emergence of unique cellular programming and gene expression profiles. Ongoing clinical studies are focused on developing novel targeted therapeutic approaches for this high-risk, lethal subset of disease, to improve on the limited durations of response often observed with traditional platinum-based chemotherapy. Neuroendocrine prostate cancer (NEPC) encompasses various clinical contexts, ranging from the de novo presentation of small cell prostatic carcinoma to a treatment-emergent transformed phenotype that arises from typical adenocarcinoma of the prostate. The development of resistance to potent androgen receptor signaling inhibition may be associated with the emergence of aggressive phenotype, advanced castration-resistant NEPC. Clinically, small cell prostate cancer and NEPC are often manifested by the presence of visceral or large soft tissue metastatic disease, a disproportionately low serum prostate-specific antigen level relative to the overall burden of disease, and a limited response to targeting of the androgen signaling axis. These tumors are often characterized by loss of androgen receptor expression, loss of retinoblastoma tumor suppressor copy number or expression, amplification of Aurora kinase A and N-Myc, and activation of the PI3K pathway. However, a consensus phenotype-genotype definition of NEPC has yet to emerge, and molecularly based biomarkers are needed to expand on traditional morphologic and immunohistochemical markers of NEPC to fully define the spectrum of this aggressive, androgen receptor-independent disease. Emerging studies implicate a shared clonal origin with prostatic adenocarcinoma in many cases, with the adaptive emergence of unique cellular programming and gene expression profiles. Ongoing clinical studies are focused on developing novel targeted therapeutic approaches for this high-risk, lethal subset of disease, to improve on the limited durations of response often observed with traditional platinum-based chemotherapy.

Treatment options for advanced thyroid cancer refractory to standard therapies are limited. The safety and efficacy of pembrolizumab were evaluated in patients with advanced differentiated thyroid cancer expressing programmed death ligand 1 (PD-L1). Patients with advanced thyroid cancer were enrolled in the nonrandomized, phase Ib KEYNOTE-028 trial conducted to evaluate safety and antitumor activity of the anti–programmed death 1 (PD-1) antibody pembrolizumab in advanced solid tumors. Key eligibility criteria were advanced papillary or follicular thyroid cancer, failure of standard therapy, and PD-L1 expression in tumor or stroma cells (assessed by immunohistochemistry). Pembrolizumab 10 mg/kg was administered every 2 weeks up to 24 months or until confirmed progression or intolerable toxicity. The primary endpoint was objective response rate (ORR) per Response Evaluation Criteria in Solid Tumors, version 1.1. Twenty-two patients were enrolled: median age was 61 years; 59% were women; and 68% had papillary carcinoma. Median follow-up was 31 months (range, 7–34 months). Treatment-related adverse events were observed in 18 (82%) patients; those occurring in ≥15% of patients were diarrhea (n = 7) and fatigue (n = 4). One grade ≥ 3 treatment-related adverse event occurred (colitis, grade 3); no treatment-related discontinuations or deaths occurred. Two patients had confirmed partial response, for an ORR of 9% (95% confidence interval [CI], 1–29%); response duration was 8 and 20 months. Median progression-free survival was 7 months (95% CI, 2–14 months); median overall survival was not reached (95% CI, 22 months to not reached). Results of this phase Ib proof-of-concept study suggest that pembrolizumab has a manageable safety profile and demonstrate evidence of antitumor activity in advanced differentiated thyroid cancer in a minority of patients treated. Further analyses are necessary to confirm these findings. Clinicaltrials.gov identifier: NCT02054806 . Registered 4 February 2014.

Purpose: ZEN-3694 is a bromodomain extraterminal inhibitor (BETi) with activity in androgen-signaling inhibitor (ASI)-resistant models. The safety and efficacy of ZEN-3694 plus enzalutamide was evaluated in a phase Ib/IIa study in metastatic castration-resistant prostate cancer (mCRPC).Patients and Methods: Patients had progressive mCRPC with prior resistance to abiraterone and/or enzalutamide. 3+3 dose escalation was followed by dose expansion in parallel cohorts (ZEN-3694 at 48 and 96 mg orally once daily, respectively).Results: Seventy-five patients were enrolled (N = 26 and 14 in dose expansion at low- and high-dose ZEN-3694, respectively). Thirty (40.0%) patients were resistant to abiraterone, 34 (45.3%) to enzalutamide, and 11 (14.7%) to both. ZEN-3694 dosing ranged from 36 to 144 mg daily without reaching an MTD. Fourteen patients (18.7%) experienced grade ≥3 toxicities, including three patients with grade 3 thrombocytopenia (4%). An exposure-dependent decrease in whole-blood RNA expression of BETi targets was observed (up to fourfold mean difference at 4 hours post–ZEN-3694 dose; P ≤ 0.0001). The median radiographic progression-free survival (rPFS) was 9.0 months [95% confidence interval (CI), 4.6–12.9] and composite median radiographic or clinical progression-free survival (PFS) was 5.5 months (95% CI, 4.0–7.8). Median duration of treatment was 3.5 months (range, 0–34.7+). Lower androgen receptor (AR) transcriptional activity in baseline tumor biopsies was associated with longer rPFS (median rPFS 10.4 vs. 4.3 months).Conclusions: ZEN-3694 plus enzalutamide demonstrated acceptable tolerability and potential efficacy in patients with ASI-resistant mCRPC. Further prospective study is warranted including in mCRPC harboring low AR transcriptional activity.