Chicago, Illinois—According to research being presented at the ASCO 2019 Annual Meeting, treatment with pembrolizumab plus enzalutamide showed sustained activity in abiraterone-pretreated, chemotherapy-naïve patients with metastatic castrate resistant prostate cancer (mCRPC).

“Pembro[lizumab] has activity as monotherapy in pts [patients] with pretreated advanced mCRPC. A phase 2 study suggested that pembro + enza [pembrolizumab plus enzalutamide] after progression on enza [enzalutamide] may have clinical activity,” said lead investigator Peter C.C. Fong, FRACP, MBBS, Consultant Medical Oncologist, Auckland Hospital and Canopy Cancer Care, and colleagues.

Dr Fong et al examined 69 chemotherapy-naïve patients with mCRPC who were unresponsive to or became intolerant of ≥4 weeks of abiraterone therapy, with prostate-specific antigen (PSA) or radiologic progression within 6 months of being screened for the trial. Participants in the study received pembrolizumab 200 mg intravenously every 3 weeks with oral enzalutamide 160 mg daily. 

The primary end points of the study included safety and PSA response rate (ie, confirmed PSA decrease ≥50%), and key secondary end points were investigator-assessed overall response rate (ORR), disease control rate (DCR), time to PSA progression, and overall survival (OS).

The median age of the patients included in the study was 69 years; 26% had visceral disease and 36% had measurable disease. The median follow-up time was 9 months.

Findings demonstrated a median duration of response of 8.3 months, with 3 (75%) patients achieving a duration of response ≥6. In patients with measurable disease, time to confirmed PSA progression was a median of 18 weeks (95% CI, 15-48).

In addition, 50% of patients with measurable disease had no confirmed PSA progression at 27 weeks. The median OS was not reached.

According to Dr Fong and his co-investigators, treated-related adverse events occurred in 63 (91%) patients. The most frequently reported adverse events included fatigue (30%), rash (23%), and nausea (22%). Furthermore, grade 3/4 treatment-related adverse events occurred in 28 (41%) patients. Importantly, there were no deaths from treatment-related adverse events.

“The [pembrolizumab plus enzalutamide] combination showed sustained activity in [abiraterone]-pretreated chemotherapy-naive mCRPC,” concluded Dr Fong and his coauthors.

“[Adverse events] were considered tolerable for the treatment combination; incidence of rash resolved with standard-of-care treatment,” they added.—Julie Gould

Fong PCC, Retz M, Drakaki A, et al. Pembrolizumab (pembro) plus enzalutamide (enza) in abiraterone (abi)-pretreated patients (pts) with metastatic castrate resistant prostate cancer (mCRPC): Cohort C of the phase 1b/2 KEYNOTE-365 study. Presented at: the 2019 ASCO Annual Meeting. Abstract: 5010.