GSK 219451 - POPSTAR

Phase 1:;To assess the safety and tolerability of cobolimab in combination with dostarlimab in pediatric and young adult participants with relapsed/refractory or newly diagnosed tumors.;To determine the recommended Phase 2 dose (RP2D) for the combination.;Phase 2:;To evaluate the anti-tumor activity of the combination based on objective response rate (ORR) per RECIST or other appropriate criteria.