Primary Colonic Lymphoma With Paraneoplastic Hypercalcemia

Primary colonic lymphoma is a rare tumor accounting for 0.1%–0.5% of all colorectal malignancies. We describe a 63-year-old man whose initial presentation was altered mental status due to hypercalcemia. Physical examination revealed a hard, right-sided abdominal mass. Abdominal computed tomography showed a mass in the ascending colon, which on further evaluation with colonoscopy and biopsy was diagnosed as diffuse large B-cell lymphoma. A diagnosis of primary colonic lymphoma was made based on the Dawson criteria, after ruling out any extracolonic involvement. Workup for hypercalcemia showed elevated calcitriol levels, which is a paraneoplastic manifestation of the lymphoma.