625P Pembrolizumab (pembro) plus enzalutamide (enza) in patients with abiraterone acetate (abi)-pretreated metastatic castration-resistant prostate cancer (mCRPC): KEYNOTE-365 Cohort C update

Abstract

Conclusions: OLA tolerability in mCRPC pts was consistent with other tumour types. Common AEs of anaemia, nausea, decreased appetite and fatigue/asthenia occurred early, gave no indication of cumulative toxicity, were manageable and led to few treatment discontinuations. There was insufficient evidence to confirm or refute a causal association between PE and OLA.Clinical trial identification: NCT02987543.

KEYNOTE-641: A Phase III Study of Pembrolizumab Plus Enzalutamide for Metastatic Castration-Resistant Prostate Cancer

“…The ORR for patients with measurable disease and ≥27 weeks of follow-up (n = 25) was 12% (3 of 25 patients) [52]. Median rPFS was 6 months (95% CI: 4-7) and median OS was 20 months (95% CI: 16 to not reached) [52]. The 12-month OS rate was 73% [52].…”

“…Immune-related AEs were reported in 7 patients (25%) [50]. The combination of pembrolizumab (200 mg IV every 3 weeks [Q3W]) plus enzalutamide (160 mg/day orally) is being assessed in cohorts 4 and 5 in the KEYNOTE-199 study and cohort C of the Phase Ib/II KEYNOTE-365 study (NCT02861573) [51,52]. In cohorts 4 and 5 of the KEYNOTE-199 study, patients who did or did not previously receive abiraterone acetate and for whom their current enzalutamide treatment failed after clinically meaningful response received pembrolizumab (200 mg IV Q3W) in addition to their standard of care dose of enzalutamide [51].…”

“…Two patients in cohort 4 died of immune-related AEs (Miller Fisher syndrome and myasthenia gravis). Cohort C of the KEYNOTE-365 study included patients in whom therapy failed or who became intolerant to ≥4 weeks of abiraterone acetate in the prechemotherapy mCRPC state (cohort C of KEYNOTE-365; NCT02861573) [52]. After a median time of 19 months from enrollment to data cutoff, 22 of 101 patients (22%) with PSA measurement at baseline had a confirmed PSA decrease of at least 50% [52].…”

“…Cohort C of the KEYNOTE-365 study included patients in whom therapy failed or who became intolerant to ≥4 weeks of abiraterone acetate in the prechemotherapy mCRPC state (cohort C of KEYNOTE-365; NCT02861573) [52]. After a median time of 19 months from enrollment to data cutoff, 22 of 101 patients (22%) with PSA measurement at baseline had a confirmed PSA decrease of at least 50% [52]. The ORR for patients with measurable disease and ≥27 weeks of follow-up (n = 25) was 12% (3 of 25 patients) [52].…”

“…After a median time of 19 months from enrollment to data cutoff, 22 of 101 patients (22%) with PSA measurement at baseline had a confirmed PSA decrease of at least 50% [52]. The ORR for patients with measurable disease and ≥27 weeks of follow-up (n = 25) was 12% (3 of 25 patients) [52]. Median rPFS was 6 months (95% CI: 4-7) and median OS was 20 months (95% CI: 16 to not reached) [52].…”