Background: Nivolumab, a fully human IgG4 mAb that targets programmed death-1, alone and in combination with ipilimumab, a fully human IgG1 mAb that targets cytotoxic T-lymphocyte antigen 4, has demonstrated encouraging clinical activity in patients with advanced GC. These data support the rationale that nivolumab in combination with other IO agents or targeted therapies may improve treatment outcomes in patients with advanced GC. Given the rapid development of novel IO agents, traditional studies cannot efficiently evaluate all possible IO-IO and IO-targeted therapy combinations. FRACTION is an innovative clinical trial program with a rolling, adaptive platform design that allows for the addition of new combination regimens, as well as withdrawal of ineffective regimens. Here we describe the study concept, key design components, and the first IO treatment combinations of FRACTION-GC, a phase 2, randomized, open-label, adaptive study in advanced GC (NCT02935634). Methods: Patients with advanced GC or gastroesophageal junction (GEJ) cancer will be enrolled based on prior IO treatment and randomized to receive nivolumab plus BMS-986016 (fully human IgG4 mAb that targets lymphocyte activation gene 3) or nivolumab plus ipilimumab. Enrollment is continuous and may offer patients consecutive treatment options based on their treatment exposure and response. The primary endpoints are objective response rate, duration of response, and progression-free survival rate at 24 weeks. The secondary endpoint is safety. Comprehensive biomarker analyses will also be performed. New treatment combinations will be added over time to explore their potential benefits and to provide a continuous flow of treatment options for patients whose cancer progresses on existing treatments. In this way, FRACTION-GC is envisioned to accelerate the development of the next generation of IO combinations for patients with metastatic GC and GEJ cancer. Clinical trial information: NCT02935634