A Gut Feeling: Mantle Cell Lymphoma Unveiled by Occult Gastrointestinal Bleeding in a 75-Year-Old Woman: A Case Report and Literature Review

Background Mantle cell lymphoma (MCL) is a rare form of non-Hodgkin lymphoma that frequently involves extranodal sites, particularly the gastrointestinal (GI) tract. While GI involvement is common in MCL, presentation with overt GI bleeding as the primary manifestation is uncommon and poses significant diagnostic challenges. Case Presentation: We report a case of a 75-year-old woman with a history of hypothyroidism and hemorrhoids who presented with generalized weakness, dyspnea, and abdominal pain. She denied overt signs of GI bleeding but reported poor appetite and unintentional weight loss over several months. Laboratory studies revealed severe anemia (hemoglobin 5.4 g/dL) and thrombocytopenia. Imaging demonstrated large left pleural effusion, hepatosplenomegaly, splenic lacerations, and lymphadenopathy. Upper endoscopy and colonoscopy revealed multiple gastric ulcers, ulcerated duodenal polypoid lesions, transverse colon polyp, and rectal polypoid lesions. Histopathological examination confirmed mantle cell lymphoma with a characteristic immunohistochemical profile. The patient was initiated on combination therapy with rituximab, bendamustine, and acalabrutinib. Conclusion This case highlights the importance of considering MCL in elderly patients presenting with unexplained anemia and constitutional symptoms, even without overt GI bleeding. Comprehensive endoscopic evaluation with systematic biopsies is crucial for diagnosis, and modern chemoimmunotherapy regimens can improve outcomes in this challenging patient population.