KEYNOTE-365: Pembrolizumab With AAP in mCRPC

In a poster featured at the ESMO Congress 2022, Mark Linch reported 2-year follow-up data from cohort D of the KEYNOTE-365 study on pembrolizumab plus abiraterone acetate and prednisone in chemotherapy-naïve patients with metastatic castration-resistant prostate cancer (mCRPC).

According to Linch, in the 10.6 months since the interim analysis, pembrolizumab plus abiraterone continued to exhibit antitumor activity with an acceptable safety profile in this population; however, Linch did note that the incidence of grade 3-4 alanine aminotransferase (ALT) or aspartate aminotransferase (AST) elevations was higher compared with pembrolizumab or abiraterone acetate alone.

KEYNOTE-365 enrolled patients with mCRPC with no prior chemotherapy or next-generation hormonal agents (NHAs)—unless patients were intolerant to or progressed on enzalutamide. The primary end points included safety, prostate-specific antigen (PSA) response rate, and objective response rate (ORR) according to RECIST 1.1 criteria.

The completed analysis included 103 patients with a median treatment time of 28.2 months (range, 20.2-37.6) from first dose to the February 14, 2022, data cutoff. Among all patients, 35.9% had RECIST-measurable disease, 72.8% had no prior NHAs, and 6.2% had prior enzalutamide.

Overall, 56.3% of patients had a confirmed PSA response, and 78.6% had a confirmed or unconfirmed reduction from baseline PSA. Median radiographic progression-free survival (rPFS) was 15.1 months (95% CI, 9.2-22.2), 24-month rPFS was 33.3%, median overall survival (OS) was 29.7 months (95% CI, 23.3-not reached), and 36-month OS was 49.5%.

The ORR was 16.2% in patients with RECIST-measurable disease (1 complete response [CR]; 5 partial responses), 21.7% in those with no prior NHAs, and 7.7% in those with prior enzalutamide. Two patients with non-measurable disease per RECIST achieved CR.

Notably, median duration of response in all responders was not reached (range, 2.1+ to 24.4+). The disease control rate was 44.7% in all patients, 58.7% in those with no prior NHAs, and 7.4% in those with prior enzalutamide.

Treatment-related adverse events occurred in 91.3% of patients, and grade 3-5 events occurred in 38.8%. Grade 3 or 4 ALT or AST elevation occurred in 18.4% and 12.6% of patients, respectively, and 1 patient died due to treatment-related myasthenic syndrome.

Linch and colleagues noted the complete KEYNOTE-365 data continued to demonstrate the potential value of pembrolizumab plus abiraterone acetate and prednisone in patients with mCRPC.

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