IOLite: Multipart, phase 1b, dose-finding study of the PD-1 inhibitor dostarlimab in combination with the PARP inhibitor niraparib ± bevacizumab (bev), or with platinum-based chemotherapy ± bev for advanced cancer.

2560 Background: Novel combinations of drugs may overcome resistance in patients (pts) with solid tumors who had progressed on standard therapy. Methods: IOLite (NCT03307785) is a multicenter, open label, multipart study to determine dosing and evaluate safety and efficacy of dostarlimab in combination with approved therapies in pts with advanced solid tumors. Pts were enrolled in each part based on tumor histology, prior treatment (tx) history, and physician preference. Primary endpoint is dose-limiting toxicities (DLTs) deemed as tx-related per investigator, and safety and tolerability of the combination. Tumor responses were assessed per RECIST v1.1. Results: Parts A-D (see Table) are fully enrolled. One complete response was reported in part B (endometrial); confirmed partial responses in part A (ovarian, small cell lung [SCLC], gastrointestinal stromal [GIST]); part B (breast [2], bladder, SCLC); part C (prostate, fallopian tube), and part D (endometrial, non-SCLC). Stable disease was reported in part A (colorectal, prostate [2], breast, GIST, gastric); part B (SCLC, squamous cell, head and neck, prostate); part C (pancreatic, ovarian, GIST, breast [2], liver, endometrial); part D (ovarian, head & neck, cholangiocarcinoma). At data cutoff, 24 pts remain on treatment. PK’s of dostarlimab and niraparib (nir) were not altered by any of the combination agents tested. Conclusions: Dostarlimab is well tolerated in combination with nir ± bev, or carbo-pac ± bev. Preliminary efficacy data show responses in various histologies. No new safety signals were identified. Clinical trial information: NCT03307785. [Table: see text]