[CD20-negative diffuse large B-cell lymphoma complicated by rheumatoid arthritis]

CD20 antigen is an important marker for diagnosis of B-cell neoplasms that is highly expressed on the surface of neoplastic B lymphocytes. Patients with rheumatoid arthritis (RA) have an increased risk of developing malignant lymphoma, of which diffuse large B-cell lymphoma (DLBCL) is the most common type. We report an unusual case of CD20-negative DLBCL complicated by rheumatoid arthritis. An 81-year old female presented with a left-sided cervical tumor, enlarged tonsil, and polyarticular pain. Pathological findings of the left tonsil showed proliferation of large atypical cells with irregular shaped nuclei. Most large cells were negative for CD3 and CD20. Additionally, these cells were positive for CD79a, BCL2, and MUM1, and negative for CD10, CD138, BCL6, PAX5, EBV-ISH, HHV8, and ALK.. Therefore, she was diagnosed with CD20-negative DLBCL complicated with RA and received dose-modified CHOP that achieved partial remission. Because CD20-negative DLBCL is rare, the identification of the clinicopathological features of this disease is urgently required.