A major gene that is involved in causing colorectal cancer. APC is involved in both sporadic and familial forms of colorectal cancer. A mutation in the APC gene is the earliest detectable molecular abnormality in colorectal cancer. This mutation imitates the neoplastic process 20 to 30 years before the malignancy itself is full-blown. APC is a relatively large gene on chromosome 5 in region 5q21-q22. Although a number of different mutations have been identified in the APC gene, most (about 80%) of them cluster in one area of the gene, interrupt its transcription, and truncate (cut off) the transcript. APC stands for adenomatous polyposis coli.