Prostate Oncology Specialists, Marina Del Rey, CA
Juliana Higa , Kirk Wilenius , Joanne B. Weidhaas , Claire Larsen , Richard Y. Lam , Jeffrey Turner , Mark C. Scholz
Background: Two previous Phase II trials studying pembrolizumab (Pembro) in 38 patients suggest it may be efficacious for prostate cancer (PC). Methods: Fifty-four consecutive men with recurrent or advanced prostate cancer were treated with 1 to 9 cycles of Pembro 200 mg every 3 weeks with or without SBRT at a private medical oncology clinic specializing in PC. Charts were retrospectively reviewed for response and toxicity. Definitions: Response (R) = >50% PSA decline; Progressive Disease (PD) = >50 % PSA increase. Stable Disease (SD)= neither response or progression. Results: 43 men completed 3 cycles of Pembro and were evaluable for toxicity. Toxicity was comparable to reports with other cancers besides PC, with 30.2% (13/43) having Grade 2 or higher toxicity. 31 men completed 4 cycles of Pembro and were evaluable for response. For the 31, the median Gleason score was 4+4=8. Treatment prior to Pembro was enzalutamide (26), abiraterone (18), and sipuleucel-t (23) and docetaxel (20). All but 4 men were castrate resistant (CRPC). Ten men got SBRT to a metastasis shortly before or during Pembro. Number of mutations were determined by the Guardant 360 assay. 17/31 (55%) were responders (19%) or had stable disease (35%). Characteristics of the two subgroups, R (6/31) + SD (11/31) versus PD (14/31), are presented in the table. Conclusions: Disease stabilization or response occurred in slightly more than half of the men treated with 4 or more cycles of Pembro. These positive responses were more common in men with lower PSA, fewer bone mets, fewer mutations, less previous chemotherapy, and there was a trend toward greater benefit in castrate sensitive disease and older men. In a separate abstract related to this patient cohort, the predictive ability of inherited mutations disrupting microRNA signaling were assessed for their capacity to predict toxicity (n=40). The table shows medians of the subgroups in the left 5 columns and the total number of patients in the right 3 columns for the 31 patients evaluable for response.
Age | Base PSA | Base PSA-DT | # of Bone Mets | Number of Mutations | CRPC | Previous Chemo | SBRT | |
---|---|---|---|---|---|---|---|---|
Total: n= 31 | 75 | 8.1 | 5.4 | 3 | 2 | 27 | 20 | 10 |
R + SD: n=17 | 77 | 3.9 | 5.9 | 1 | 2 | 13 | 8 | 7 |
PD: n=14 | 73 | 27.8 | 4.1 | 6 | 3.5 | 14 | 12 | 3 |
P value | 0.065 | 0.049 | NS | 0.022 | <0.01 | 0.052 | 0.025 | NS |
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