Solstice Oncology emerged from stealth with a $225 million Series A to advance porustobart, a next-generation CTLA-4 antibody designed for immunotherapy use in microsatellite-stable (MSS) colon cancer. The CTLA-4 asset stems from a China-origin licensing anchor from Harbour Biomed. The financing is expected to fund a Phase 2 study evaluating porustobart plus pembrolizumab in stage II–III MSS colon cancer in the neoadjuvant setting, with enrollment planned for Q4 2026 and an initial readout targeted for the second half of 2027. Backers included RA Capital Management, Canaan Partners, and Forbion. For the sector, the launch matters because it reflects ongoing investor appetite for checkpoint combinations aimed at expanding benefits beyond MSI-high disease. It also spotlights the continued use of cross-border licensing pathways to accelerate clinical timelines in immuno-oncology.