2756 Metastatic Gastric Neuroendocrine Tumors in Non-Surveillanced Familial Adenomatous Polyposis

INTRODUCTION: Familial adenomatous polyposis (FAP) accounts for 1% of colorectal cancers (CRC), and if left untreated, has a 100% lifetime probability of developing CRC. Close monitoring is required to mitigate effects. Though rarely reported in literature, neuroendocrine tumors are also noted to occur in FAP despite adenomatous predominance. Our case report describes a patient diagnosed with FAP that underwent prophylactic colectomy and initial treatment, and then decided to cease screening. 16 years later, she presented with metastatic disease arising from a gastric source of neuroendocrine origin. We highlight a rare case of gastric neuroendocrine tumor in FAP without surveillance, a less-understood disease process. CASE DESCRIPTION/METHODS: We present a case of a 38-year-old female with a past medical history of FAP diagnosed at age 22. She underwent prophylactic colectomy with internal ileostomy and treated for several years with imatinib; however, she stopped medication due to side effects, and chose to end routine surveillance. She presented with acute abdominal pain 16 years later, with physical exam findings of abdominal distension, epigastric tenderness, and palpable liver. CT abdomen/pelvis showed gastric mass, innumerable liver masses, and rectal masses. EGD revealed innumerable polyps carpeting entirety of stomach extending into duodenum, and a 5.3cm ulcerated gastric mass. Colonoscopy demonstrated diffuse polyps through the neo-rectal vault and anal canal. Multiple samples were obtained for study, including liver biopsy. Pathology revealed primary gastric neuroendocrine carcinoma with metastasis to liver, while rectal polyps were tubular adenomas. Whole-body imaging did not show any further spread. The patient was informed of her poor prognosis, and opted for discharge on palliative chemotherapy. DISCUSSION: A genetic risk for CRC exists in FAP patients, though they can also develop other cancers, as did our patient. Our case is unique in that a metastatic neuroendocrine gastric tumor in FAP has seldom been reported. An added angle of interest derives from the patient declining standard surveillance, which may have yielded prompt detection of disease progression. However, even if identified early, the paucity of understanding between FAP and neuroendocrine tumors still exists, limiting evidenced-based instruction for intervention and treatment. An inappreciable amount of such cases reported in literature means the association is poorly understood and warrants further study for clinical guidance.