- Pembrolizumab monotherapy was well tolerated and shows activity in a subset of patients with bone-predominant metastatic castration-resistant prostate cancer (mCRPC) previously treated with docetaxel+targeted endocrine therapy.
Why this matters
- Promising OS estimates indicate that pembrolizumab may extend survival in these difficult-to-treat patients.
- Phase 2 KEYNOTE-199 study of 199 patients with mCRPC previously treated with docetaxel and ≥1 targeted endocrine therapy who received pembrolizumab.
- Primary endpoint: objective response rate (ORR).
- Funding: MSD.
- 133 patients had PD-L1-positive disease (group 1), 66 had PD-L1-negative disease (group 2), and 59 had bone predominant disease regardless of PD-L1 expression (group 3).
- In groups 1 and 2:
- ORR was 5% (95% CI, 2%-11%) and 3% (95% CI,
- Median duration of response was not reached (range, 1.9 to ≥21.8 months) and 10.6 (range, 4.4-16.8) months, respectively.
- In groups 1, 2, and 3:
- Disease control rate was 10%, 9%, and 22%, respectively.
- Median PFS was 2.1, 2.1, and 3.7 months, respectively.
- Median OS was 9.5, 7.9, and 14.1 months, respectively.
- 60% of patients experienced treatment-related adverse events (TEAEs); grade 3-5 TEAEs occurred in 15% of patients.
- TEAE-related discontinuation rate was 5%.
- No randomization.
- Open-label design.