Monoclonal gammopathy after low-grade MALT lymphoma: evidence for a second neoplasm

We report the case of a patient with lymphoma of the salivary gland, at first diagnosed as lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) but later found to infiltrate the bone marrow. At diagnosis, the patient had a polyclonal increase of gamma-globulins. Five years after initial diagnosis, the patient presented with monoclonal gammopathy and infiltration of the bone marrow with neoplastic cells. Initially, the patient had received chemotherapy with different protocols (including etoposide, cyclophosphamide, fludarabin, methotrexate, and vincristine), none of which induced a lasting response. Therapy with rituximab (chimeric anti-CD20 monoclonal antibody) finally led to partial remission. Eighteen months after rituximab, progressive lymphoma in the abdomen and a monoclonal gammopathy developed. The bone marrow showed infiltration by lymphoplasmacytoid cells (monoclonal expression of the light-chain type lambda, positive for CD20, heterogeneous expression of CD45). The patient achieved another short clinical response with 4 cycles of the CHOP-protocol, but soon the lymphoma progressed again. Five years and 8 months after the initial diagnosis, the patient died from septicemia and progressive lymphoma. By polymerase chain reaction (PCR) for the IgH gene it was shown that lymphoma cells were initially oligoclonal in the salivary gland and, later, biclonal in the bone marrow. Sequencing of two bands of apparently same length showed that these manifestations of lymphoma were not identical. Taken together, our data show that the initial low-grade oligoclonal MALT lymphoma was no longer present and a more aggressive biclonal lymphoma with plasmacytoid differentiation had developed. The new lymphoma was clonally distinct and produced high amounts of monoclonal IgG lambda by immunoelectrophoresis. The relationship of the second lymphoma to the initial MALT lymphoma is discussed.