KRAS and neoplasm: These differences demonstrate that in a majority of primary tumors with double mutations in KRAS and PIK3CA, the KRAS mutations are more prevalent than the PIK3CA. This unequal distribution of mutant alleles within a tumor may be due to the fact that a majority of the tumor cells have only the KRAS mutation, and cells with a PIK3CA mutation are in the minority, or it could be due to copy number variations in the KRAS and PIK3CA loci.