This is a first-in-human Phase 1/2, open-label, multicenter, dose-escalation and expansion study designed to determine the maximum tolerated dose and recommended phase 2 dose(s) and evaluate the safety and tolerability, pharmacokinetics, and antineoplastic activity of escalating oral doses of TNG260 when administered with a standard dose of pembrolizumab in participants with locally advanced or metastatic STK11 mutated solid tumors.