Keynote-365 cohort a: Pembrolizumab (pembro) plus olaparib in docetaxel-pretreated patients (pts) with metastatic castrate-resistant prostate cancer (mCRPC).

Background: Activity with pembro or olaparib has been observed in mCRPC patients who progressed on 2nd-generation hormonal therapy (HT) and chemotherapy. From KEYNOTE-365 (NCT02861573), a phase 1b/2 umbrella study testing combinations in mCRPC, we report early results from cohort A combining pembro + olaparib. 

Methods: Patients with mCRPC were eligible if they progressed within 6 months prior to screening determined by either PSA progression or radiologic progression in bone or soft tissue. Patients were docetaxel-pretreated for mCRPC, may have received 1 other chemotherapy, and had ≤2 2nd-generation HT. Pts received pembro 200 mg IV Q3W + olaparib 400 mg orally twice daily. Primary end points: safety and PSA response rate (confirmed PSA decline ≥50%). Key secondary end points: ORR RECIST v1.1 (investigator review), disease control rate (DCR: CR+PR+SD ≥6 mo), time to PSA progression, composite response rate (ORR RECIST v1.1, confirmed PSA response, or confirmed decrease in circulating tumor cell count from ≥5 to <5 cells/7.5 mL blood), rPFS, and OS. 

Results: Median follow-up was 11 mo. 41 initiated treatment (median age 69 years; PD-L1+ 27%; visceral disease 42%; RECIST-measurable 68%; homologous recombination repair mutation [HRR] 0%). See efficacy in table below. Treatment-related AEs occurred in 39 (95%) pts. Most frequent (≥30%) were anemia (37%), fatigue (34%), and nausea (34%). Grade 3-5 treatment-related AEs were in 21 (51%) pts. There were 2 deaths; only 1 was treatment-related (cause unknown). 

Conclusions: Combination of pembro + olaparib has activity in pts previously treated with docetaxel and ≤2 2nd-generation HT for mCRPC and who are HRR wild type. Observed safety profile for the combination is consistent with individual profiles of pembro and olaparib. Clinical trial information: NCT02861573.

Yu, Evan Y., Christophe Massard, Margitta Retz, Ali Tafreshi, Joan Carles Galceran, Peter Hammerer, Peter CC Fong et al. "Keynote-365 cohort a: Pembrolizumab (pembro) plus olaparib in docetaxel-pretreated patients (pts) with metastatic castrate-resistant prostate cancer (mCRPC)." (2019): 145-145.
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