Inclusion Criteria:  Histologically or cytologically confirmed diagnosis of an advanced/metastatic solid tumor Confirmed presence of a KRASG12C mutation Ineligible for an ongoing clinical trial of MRTX849 No available or not eligible for standard of care treatment Adequate organ function CNS Metastases (within set parameters) are allowed ECOG performance status of ≤ 2  Exclusion Criteria:  History of intestinal disease, inflammatory bowel disease, major gastric surgery, or other gastrointestinal conditions likely to alter absorption of MRTX849 treatment or result in inability to swallow Prior therapy targeting a KRAS G12C mutation Other active cancer