Familial adenomatous polyposis with rectal adenocarcinoma presenting as haematochezia

A Case Report

Abstract

Familial adenomatous polyposis (FAP) is a hereditary syndrome characterised by the development of hundreds to thousands of adenomatous polyps in the gastrointestinal tract. If untreated, it carries a nearly 100% lifetime risk of colorectal cancer. We report a  Filipino woman in her 40s with a one-year history of haematochezia initially misdiagnosed as grade IV internal haemorrhoids. Computed tomography revealed a rectal mass, and colonoscopy revealed rectal mass and numerous polyps throughout the colon. Genetic testing identified a pathogenic APC mutation, confirming FAP despite the absence of family history. The patient underwent exploratory laparotomy, total proctocolectomy, total mesorectal excision, and end ileostomy. This case illustrates how FAP may masquerade as a common benign anorectal disease, leading to delayed diagnosis. It further highlights the central role of genetic testing in diagnosis and the impact of healthcare access barriers in resource-limited settings. Early recognition and timely surgical management are crucial to reducing cancer risk in FAP.