Oncogenic mutations of clinical significance in colorectal cancer

Colorectal cancer (CRC) is associated with significant morbidity and mortality. Three molecular carcinogenesis pathways have been identified in CRC: chromosomal instability, microsatellite instability (MSI), and CpG island methylator phenotype. Next-generation sequencing is increasingly used in standard clinical practice to identify patients with potentially actionable mutations. Tumour biomarker expression is driving therapeutic decision-making in the treatment of metastatic CRC, with implications for both initial systemic therapy as well as subsequent treatments. Pathologists are playing an increasing role in the identification of mutations with prognostic and predictive value. Currently, testing for deficient mismatch repair/MSI, extended RAS testing, and BRAF status is recommended in all patients at the time of metastatic CRC diagnosis. This review discusses the molecular pathology of CRC including emerging potential therapeutic targets based on molecular testing.