PIK3CA and colorectal carcinoma: In colorectal cancer (CRC), molecular analysis of single CTCs revealed significant intra-patient and inter-patient heterogeneity in mutant EGFR expression as well as that of other genetic mutations relating to EGFR inhibition, such as KRAS and PIK3CA mutations, which explains the diverse response rates to EGFR-targeted therapy in patients with CRC [14].