KRAS and malignant colon neoplasm: While KRAS, APC and TP53 are frequently mutated in human colon tumors, CT26 had homozygous Kras mutations (G12D, V8M) and did not have mutations in Apc or Trp53; MC38 had Trp53 heterozygous mutations (G242 V, S258I) and a Smad4 heterozygous mutation (G351R), mutated in approximately 12% of human colon cancer, with no mutations in Kras or Apc (Table 2).