KRAS and colorectal carcinoma: Mutational inactivation of APC (adenomatous polyposis coli), a tumor suppressor gene, is considered one of the earliest events in CRC tumorigenesis and is followed by the occurrence of activating mutations in KRAS. Microsatellites are short repetitive DNA sequences that are subject to frame-shift mutations and base-pair substitutions during DNA replication and are involved in DNA repair.