Malignant Duodenal Adenoma as Extracolonic Manifestation of Familial Adenomatous Polyposis (FAP)

INTRODUCTION: Familial adenomatous polyposis (FAP) and its variants are caused by germ line mutations in the tumor suppressor gene, Adenomatous Polyposis Coli (APC). FAP is characterized by the presence of numerous colorectal adenomas and patients are usually asymptomatic until symptoms of malignancy develop. Although rare, extracolonic manifestations of FAP account for 30 to 45% of cases reported. We present a case of a 74-year-old male patient with FAP with a presentation of malignant ampullary adenoma. CASE DESCRIPTION: 74 year old AA man with PMH of HTN, DMII and FAP with sub-total colectomy, presented with abdominal bloating, left upper quadrant pain, nausea and emesis accompanied by an 11-pound weight loss over the course of 5 weeks. Physical examination revealed a hemodynamically stable patient with findings of abdominal distention and tenderness. Moderate transaminitis was noted. CT scan of the abdomen demonstrated the presence of ascitic fluid and peritoneal carcinomatosis. Upper endoscopy with biopsy revealed an irregular duodenal fold with a partially obstructing growth at the distal end of the ampulla. Pathology evaluation noted high-grade dysplasia. Signet cells with CK7, MOC31, AE1/AE3 positive markers. DISCUSSION: Extracolonic manifestations of FAP like duodenal adenomas have approximately 5% lifetime chance of progressing to duodenal cancer. When they do progress, they constitute the second most common cause of death among FAP patients. Due to the high mortality of malignant duodenal adenomas seen in FAP, early recognition is imperative in the management of patients as it can dictate treatment course and prognosis.