A phase Ia study of safety and clinical activity of atezolizumab (atezo) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC).

• DOI: 10.1200/jco.2018.36.6_suppl.187
• Publication Date: 2018-02-26T21:14:10Z
• Authors: Joseph W. Kim; David R. Shaffer; Christophe Massard; Thomas Powles; Lauren Christine ...; Fadi S. Braiteh; Paul R. Conkling; Indrani Sarkar; Edward E. Kadel; Sanjeev Mariathasan; Carol O'Hear; Christina Schiff; Marcella Fasso; Susheela Carroll; Daniel Peter Petr...
• Keywords: Atezolizumab; Enzalutamide; Tolerability

187 Background: In the past decade, several therapies have been approved for mCRPC. However, most pts develop resistance and experience disease progression. Thus, there remains a high unmet need. Atezo (anti–PD-L1) blocks interaction between PD-L1 its receptors, PD-1 B7.1, thereby restoring anti-tumor immunity. has demonstrated clinical efficacy in many tumor types. Here we report safety activity of atezo with mCRPC from Phase Ia study (PCD4989g; NCT01375842). Methods: Eligible previously received enzalutamide and/or sipuleucel-T Pts also had PSA or radiographic progression prior to enrollment. 1200mg was administered IV q3w. CT bone scans were performed q6w 24w q12w thereafter (q6w if treatment beyond progression). Primary objectives tolerability; OS an exploratory objective. cohort–specific included response, per PCWG2 criteria, soft tissue response RECIST v1.1 immune-related criteria (irRC). Survival follow-up data collected ≈ every 3 mo until death loss follow-up. Results: The 15 initial cohort evaluated (clinical cutoff: December 31, 2016). 13 (87%) ≥ 2 lines therapy Median survival 15.8 (range, 2.3-23.0). 9 (60%) treatment-related AE (TRAE); only 1 pt (7%) experienced Gr TRAE (hyponatremia). No 4-5 TRAEs reported. landmark 12-mo rate 55.6% (95% CI: 27.4, 83.7); median not reached 2.3-23.0 mo). PFS 3.4 2.3, 5.7); 6-mo 26.7% 4.3, 49.1). (9%) PR irRC (irPR); 5 (45%) SD irRC. (13%) 50% decrease baseline. who irPR increased CD8 expression expansion T-cell clones on treatment. Conclusions: well tolerated long-term control heavily pretreated mCRPC, 55.6%. Preliminary biomarker analyses suggestive activated immune response. Clinical trial information: NCT01375842.