Retz, Margitta

5029 Background: Pembro had activity as monotherapy in pretreated advanced mCRPC. Data are presented here from cohort B (pembro + docetaxel/prednisone) of KEYNOTE-365 (NCT02861573), a phase 1b/2 umbrella study to test combinations in mCRPC. Methods: Pts who progressed on or became intolerant to ≥4 wk of abi or enza in the prechemotherapy mCRPC state and progressed within 6 mo before screening were eligible. Pts received pembro 200 mg IV with docetaxel 75 mg/m2 IV Q3W plus prednisone 5 mg orally twice daily. The primary end points were safety and PSA response rate (confirmed PSA decrease ≥50%). Key secondary end points were investigator-determined ORR (RECIST v1.1), disease control rate (DCR: CR+PR+SD ≥6 mo), time to PSA progression, rPFS, and OS. Results: 72 pts (median age, 68 y; visceral disease, 36%; measurable disease, 50%) began pembro + docetaxel. Median (95% CI) follow-up was 10 (8-12) mo. Efficacy is outlined in the table. Treatment-related AEs occurred in 69 (96%) pts; most frequent (≥30%) were alopecia (43%), fatigue (40%), and diarrhea (39%). Grade 3-5 treatment-related AEs occurred in 27 (38%) pts, including 2 deaths from treatment-related AEs (pneumonitis). Most commonly reported immune-mediated AEs were infusion-related reactions (11%) and colitis (10%). Conclusions: Pembro + docetaxel/prednisone has activity in pts with mCRPC who previously progressed on second-generation hormone therapy. AEs were considered mild for the treatment combination. Clinical trial information: NCT02861573. [Table: see text]

170 Background: Pembro had antitumor activity as monotherapy in pretreated advanced mCRPC (KEYNOTE-028; KEYNOTE-199). KEYNOTE-365 (NCT02861573) is a phase 1b/2 umbrella study testing combinations in mCRPC; we report early results from cohort B combining pembro + docetaxel in mCRPC. Methods: Pts who failed or became intolerant to ≥4 weeks of abi or enza in the pre-chemotherapy mCRPC state received pembro 200 mg IV with docetaxel 75 mg/m2 IV Q3W plus prednisone 5 mg orally twice daily. Pts also progressed within 6 months prior to screening as determined by either PSA progression or radiologic progression in bone or soft tissue. Response was evaluated by PSA levels Q3W and imaging Q9W for first year and Q12W thereafter. Primary end points: safety and PSA response rate (confirmed PSA decline ≥50%). Key secondary end points: investigator-determined ORR (RECIST v1.1), disease control rate (DCR: CR+PR+SD ≥6 mo), time to PSA progression, rPFS, and OS. Results: 72 pts (median age 68 years; PD-L1+ 29%; visceral disease 36%; measurable disease 50%) initiated pembro + docetaxel. Median (95% CI) follow-up was 10 (8-12) mo. Efficacy is outlined in table below. Treatment-related AEs occurred in 69 (96%) pts; most frequent (≥30%) were alopecia (43%), fatigue (40%), and diarrhea (39%). Grade 3-5 treatment-related AEs occurred in 27 (38%) pts, including 2 deaths due to treatment-related AEs (pneumonitis). Conclusions: Combination of pembro + docetaxel/prednisone has activity in pts with mCRPC previously failing anti-hormonal therapy. Observed safety profile for the combination was consistent with known safety profile of each component. Clinical trial information: NCT02861573. [Table: see text]