PIK3CA and colorectal cancer: APC mutations, as expected for early events in colorectal cancer tumorigenesis, primarily co-occur with other mutations, most commonly with KRAS, PIK3CA and/or TP53. Because APC is a large tumor suppressor gene and OncoMap only assays for known recurrent variants, the number of mutations identified by genotyping likely under-represents the true prevalence of APC mutations in these cohorts.