APC is a tumor suppressor gene whose protein acts as a key brake on the Wnt signaling pathway by helping mark the growth-promoting protein beta-catenin for destruction; it also participates in cell migration, adhesion, and apoptosis. Inherited mutations in APC cause familial adenomatous polyposis (FAP), an autosomal dominant condition characterized by numerous colorectal polyps and a very high risk of colorectal cancer, with related forms including attenuated FAP and gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS). Somatic APC mutations are found in roughly 50-80% of sporadic colorectal cancers, where they act as early tumor-initiating events, and are also observed in some breast, stomach, and prostate cancers. Loss of APC function leaves Wnt signaling abnormally active, driving uncontrolled cell growth, which makes APC a central tumor suppressor in colorectal cancer.

As a rare 5′-UTR change in APC, a tumor-suppressor gene whose loss activates Wnt signaling and causes autosomal-dominant familial adenomatous polyposis, this variant's clinical relevance depends on whether it alters APC expression or function.