1510 Positive Fecal Immunochemical Testing in Detection of Mantle Cell Lymphoma With Gastrointestinal Involvement

Abstract

INTRODUCTION: Current colorectal cancer (CRC) screening guidelines are directed at early detection of adenocarcinoma via stool testing or direct endoscopic or radiologic visualization. Compared to a colonoscopy, fecal immunochemical Testing (FIT), a non-invasive test that detects hemoglobin in stool by immunoassay, has similar CRC detection rates. We report a case of mantle cell lymphoma (MCL) involving the gastrointestinal tract (GIT) in a patient diagnosed through routine CRC screening. CASE DESCRIPTION/METHODS: A 70 year-old male with a history of diverticulitis was referred for urgent colonoscopy following a positive FIT. He reported a seven-month history of right upper quadrant abdominal pain, pruritus, and a 19 pound unintentional weight loss. He denied fever, night sweats, melena, hematochezia, and family history of malignancy. Physical exam did not reveal splenomegaly and lymphadenopathy. Notable labs included normocytic anemia and a normal LDH. Colonoscopy showed congested, nodular and thickened mucosal folds in the terminal ileum, ascending colon, and cecum. Random biopsies revealed diffuse atypical lymphoid infiltrates in a multiple lymphomatous polyposis pattern with cyclin D1, CD5 and CD20 immunohistochemical positivity consistent with MCL. PET-CT detected bone marrow and diffuse lymph node involvement. He tolerated six cycles of lymphoma-directed chemotherapy with complete metabolic response on imaging. DISCUSSION: Extranodal disease at primary presentation accounts for 25% of patients with MCL. Microscopic gastrointestinal involvement in MCL at presentation is widely underestimated and has been documented in up to 80% of cases at the time of diagnosis, suggesting that MCL has a propensity to home to the GIT. Clinically, most patients with MCL with GIT involvement are asymptomatic, but can also present with abdominal pain, altered bowel habits, and gastrointestinal bleeding. To date, annual FIT testing has been used solely as a screening test for CRC. The role of non-invasive stool testing such as FIT, and its detection of other primary malignancies involving the gastrointestinal tract besides CRC, has not been studied and requires further investigation.