A Study to Learn About Study Medicine ALTA3263 in Adults With Advanced Solid Tumors With KRAS Mutations

The purpose of this study is to characterize the safety and tolerability of ALTA3263 in adults with advanced solid tumors with KRAS mutations.

Inclusion Criteria: * Histologically confirmed diagnosis of a solid tumor malignancy harboring a KRAS mutation identified through molecular testing (NGS- or PCR-based) with a Clinical Laboratory Improvement Amendments-certified (or equivalent) diagnostic test. * Unresectable or metastatic disease. * Progressed on, intolerant to, or declined prior standard-of-care therapy (including targeted therapy, if applicable) appropriate to tumor type and stage * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. * Adequate organ function Exclusion Criteria: * Prior treatment with a KRAS inhibitor, certain exceptions are described in the full study protocol * Known condition that prohibits the ability to swallow or absorb an oral medication. Other inclusion/exclusion criteria may apply.