Familial adenomatous polyposis (FAP) is responsible for <1% of colorectal cancer (CRC) cases and is inherited as an autosomal dominant trait. Patients generally present hundreds to thousands of adenomas and develop colorectal cancer by age 35- 40 if left untreated. Here we report four patients with germline frameshift mutation (small deletion) at exon 15 of adenomatous polyposis coli (APC) tumo...