Plasma cell leukemia with rouleaux formation involving neoplastic cells and RBC.

which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. A 77-year-old man visited our hospital complaining of fever, excessive sputum production, and dyspnea. immature plasma cells (plasmablasts), accounting for 58% of the leukocytes, and marked rouleaux formation (A). Interestingly, rouleaux formation of the neoplastic cells was also noted (B). Bone marrow study showed plasmablasts, accounting for 93% of all nucleated cells. Serum protein electrophoresis and immunotyping revealed a monoclonal peak of IgG and lambda light chain type. The amount of M-protein was 6.0 g/dL. High-resolution computed tomo-graphy of both lungs revealed multifocal consolidations with fuzzy marginated centrilobular pattern nodules, which were consistent with the findings in multifocal bronchopneumonia. Plasma cell leukemia is a variant of plasma cell myeloma with clonal plasma cell numbers in peripheral blood exceeding 2.0×10 9 /L or 20% of the leukocyte differential count. Rouleaux formation, involving the stacking of RBCs upon one another so that they resemble a stack of coins, is particularly marked in paraproteinemia. The patient showed a rouleaux formation involving not only RBCs but also neoplastic cells.