KRAS and colorectal cancer: The Schell classification for a patient’s colorectal cancer is based on the combination and number of mutations in the colorectal cancer driver genes APC, TP53, and KRAS. While TP53, KRAS, and NRAS are routinely tested for mutations, APC is not yet generally tested, despite the high frequency of mutant APC. About 80% of sporadic colorectal cancers harbor truncating mutations in APC (frameshift, nonsense, and splice site mutations), which lead to polyposis originating from single epithelial stem cells in the colonic crypt that ultimately progresses to cancer [5,6].