Composite lymphoma: a unique case with two immunologically distinct B-cell neoplasms.

The authors recently have encountered a unique case of composite lymphoma arising in a 69-year-old man with severe long-standing rheumatoid arthritis. The neoplasm was composed of two B-cell lymphomas occurring within a single axillary lymph node: nodules of IgG-kappa nodular poorly differentiated lymphocytic lymphoma were surrounded by a diffuse growth of IgM-lambda well-differentiated lymphocytic lymphoma. It was the immunohistologic studies performed in this case that demonstrated the simultaneous occurrence of two separate monoclonal lymphocyte proliferations. Without the immunohistologic procedures, this composite lymphoma easily may have been overlooked. This unusual malignancy arose in the background of a long-standing autoimmune disease that may have played a role in its genesis.