Association of neuroendocrine phenotype with platinum chemotherapy outcomes in men with metastatic prostate cancer.
e16532 Background: DNA repair defects are common in men with mCRPC, and platinum chemotherapy may have a role in selected patients. We aimed to determine whether neuroendocrine variant prostate cancer (NEPC) is associated with a greater response to platinum chemotherapy, as compared to CRPC with adenocarcinoma histology (AdenoCRPC). Methods: We conducted a retrospective cohort analysis of all patients with prostate cancer treated with platinum chemotherapy at the Duke Cancer Center between 2005-15. The primary endpoint was objective response rate (RESIST v1.1; ORR); secondary endpoints were PSA decline, progression-free (PFS) and overall survival (OS). Outcomes were compared by histologic phenotype (NEPC vs. AdenoCRPC). Results: Between 2005-2015, 73 men, including 56 with AdenoCRPC and 17 with NEPC, were treated with platinum-based chemotherapy for mCRPC. Carboplatin-docetaxel and carboplatin/cisplatin etoposide were the most common regimens. Fifteen men (21%) were M1 at diagnosis. Among NEPC patients, 3 had primary NEPC/small cell carcinoma at diagnosis, while 14 had NEPC transformation after hormonal therapy. Overall, 24% of NEPC men received prior docetaxel vs. 75% of AdenoCRPC men. Partial responses were observed in 59% in men with NEPC vs. 25% for AdenoCRPC. Primary progressive disease occurred in 24% (NEPC) vs. 48% (AdenoCRPC). PSA declines with platinum chemotherapy were more common in NEPC (median 72% decline) vs. AdenoCRPC (median 24% decline). There was no significant difference in median PFS or OS between phenotypes (NEPC PFS 5.1 mo, OS 8.5 mo; AdenoCRPC PFS 4.3 mo, OS 10.0 mo; p = NS). For second platinum chemotherapy, ORR and PFS in NEPC vs AdenoCRPC were 67% and 5.2 months vs. 14% and 4.6 months. Conclusions: Our data suggest that men with NEPC histology have a greater probability of objective response and PSA decline with platinum chemotherapy vs. men with AdenoCRPC. However, PFS and OS are similar across histologic phenotypes, indicating similar times to resistance to platinum chemotherapy. Biomarkers of platinum sensitivity are needed, and evaluation of DNA repair defects in this setting may provide a greater opportunity for precision medicine approaches to DNA damaging agents.
Humeniuk, MS; Gupta, RT; McNamara, MA; Ramalingam, S; Harrison, MR; George, DJ; Wu, Y; Healy, P; Armstrong, AJ
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