Primary pulmonary plasmacytoma involving bilateral lungs and marked hypergammaglobulinemia: differentiation from extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue.

A 71-year-old woman was referred to our hospital because of hyperproteinemia and serum M-protein (IgG-lambda type). Chest computed tomographic (CT) scan revealed a tumor in each lung and transbronchial lung biopsy was performed. Histopathological examination showed monotonous medullary proliferation of morphologically mature plasma cells. These cells were cIgG+, cIg-lambda+, CD 20+, CD 79 a+, CD 138+, cIg-kappa-, and CD3-. Since there were very few non-neoplastic plasma cells and small lymphocytes in addition to the absence of reactive lymph follicles and fibrosis, the patient was diagnosed as having plasmacytoma. There was no proliferation of plasma cells in the bone marrow. Thus, the lesion was finally characterized as primary pulmonary plasmacytoma. Treatment with melphalan/prednisolone resulted in considerable decrease in the serum IgG level and regression of the pulmonary tumors. The effectiveness of the chemotherapy could confirm our diagnosis, although MALT-type lymphoma with plasmacytic differentiation cannot be completely ruled out.