PD‐1 Inhibition with Retifanlimab And/or Arginase Inhibition with INCB001158 in Japanese Patients with Solid Tumors: A Phase I Study

AbstractBackgroundRetifanlimab is a humanized monoclonal antibody targeting programmed death protein‐1, and INCB001158 is an oral arginase inhibitor. This phase Ib study investigated retifanlimab, INCB001158, and their combination in Japanese patients with advanced solid tumors.MethodsPatients received retifanlimab (500 mg every 4 weeks [Q4W] i.v.) or escalating doses of INCB001158 (75 or 100 mg twice daily [BID]) monotherapy in Part 1 and combination of retifanlimab (500 mg Q4W) and INCB001158 (100 mg BID) in Part 2. Primary endpoints were safety, tolerability, dose‐limiting toxicities (DLTs), and determination of recommended phase II doses in Japanese patients.ResultsEighteen patients (retifanlimab or INCB001158 monotherapy and combination; n = 6 each) were enrolled at 2 sites in Japan. There were no DLTs, fatal adverse events (AEs), or discontinuations due to AEs. Rash (all grade 1) was the most common treatment‐emergent AE with retifanlimab (n = 6). Treatment‐related AEs were reported with retifanlimab (n = 4) or INCB001158 (n = 2) monotherapy and with combination (n = 4); an immune‐related AE (thyroid disorder, grade 2) was reported with combination. Two responses were observed with retifanlimab monotherapy (1 complete, 1 partial) and 1 stable disease (SD), for an overall response rate of 33.3% (95% confidence interval [CI], 4.3–77.7) and disease control rate (DCR) of 50% (95% CI, 11.8–88.2). Three patients had SD with INCB001158 monotherapy (DCR 50%; 95% CI, 11.8–88.2). No responses or SD were observed with combination therapy.ConclusionRetifanlimab, INCB001158, and their combination had acceptable safety profiles. Promising retifanlimab antitumor activity warrants further investigation in Japanese patients.