Pembrolizumab Plus Lenvatinib in Participants with Docetaxel-pretreated Metastatic Castration-resistant Prostate Cancer: Results from KEYNOTE-365 Cohort E

: Pembrolizumab has shown manageable safety and modest antitumor activity when used as a single agent in participants with metastatic castration-resistant prostate cancer (mCRPC). Preclinical evidence suggests that lenvatinib, a vascular endothelial growth factor-targeted agent, inhibits angiogenesis and cell migration in prostate cancer. Safety and efficacy of pembrolizumab plus lenvatinib in participants with docetaxel-pretreated mCRPC were evaluated in cohort E of the phase 1b/2 KEYNOTE-365 study. Eligible adults with confirmed mCRPC, Eastern Cooperative Oncology Group performance status (ECOG PS) scores of 0 or 1, and prior docetaxel treatment for mCRPC received pembrolizumab 200 mg intravenously every 3 wk, for ≤35 cycles, plus oral lenvatinib 20 mg daily, continuously from day 1 of cycle 1, unless specific discontinuation criteria were met. Primary endpoints were prostate-specific antigen (PSA) response rate; objective response rate (ORR), per Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST) v1.1, by blinded independent central review; and safety. A total of 39 participants received treatment, with a median follow-up of 9.7 mo (interquartile range, 8.5-11.3). Confirmed PSA response rate was 34% (95% confidence interval [CI], 20-51). ORR for participants with RECIST-measurable disease was 36% (95% CI, 18-57). Treatment-related adverse events (AEs) of any grade occurred in 92% of participants and grade 3-5 treatment-related AEs occurred in 62% of participants. Two participants died of non-treatment-related AEs (acute kidney injury and unspecified death). Clinical trial registry: NCT02861573.