Relapsed Multiple Myeloma in the Gastrointestinal Tract With Aberrant Expression of CD3: A Case Report

This report describes a rare case of relapsed multiple myeloma in the gastrointestinal tract with aberrant CD3 expression. Upon admission for acute renal failure, the patient had abnormal computed tomography scan findings of the abdomen and pelvis. Subsequent colonoscopy found numerous polyps and masses. Histologic examination of a biopsy of one of the masses revealed a diffuse atypical cellular infiltrate with undifferentiated morphology in the submucosa that was positive for CD3, CD4, weak and variable CD79a, CD138, BCL2, CMYC, MUM1, vimentin, and monoclonal cytoplasmic lambda. A diagnosis of recurrent plasma cell myeloma was made. The positive expression of T-cell markers CD3 and CD4 may cause confusion with T-cell lymphoma in a scenario with undifferentiated morphology as in our case.