A Study to Learn About Study Medicine 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.