#00060567

A 69-year-old male was referred for plasma cell myeloma (PCM) two years previous to current presentation. He had mild anemia, IgG kappa paraprotein (3.0 g/dL), and multiple lytic lesions.  Bone marrow showed atypical plasma cells; a subset had prominent central nucleoli (A and B).  The core biopsy was 50% cellular with 60% kappa-restricted plasma cells.  Flow phenotype showed a plasma cell population positive for CD138, CD38, and CD56 and negative for CD45, CD19, and CD20.  Cytogenetics revealed a complex karyotype.  Treatment with Velcade, Revlimid, and dexamethasone yielded good response.

At current follow-up, the patient was pancytopenic with a serum paraprotein of 0.4 g/dL.  Bone marrow aspirate revealed sheets of atypical, small to intermediately-sized cells with high-grade features, including high nuclear to cytoplasmic ratio, “hard-mirror” cytoplasmic projections (C; arrow), and prominent nucleoli.  The biopsy was 30% cellular with an infiltrate of cells with scant cytoplasm and prominent nucleoli (D).  By flow cytometry, the atypical cells expressed CD138, CD38, and CD56 with heterogeneous expression of CD45 and CD20.

The morphologic features and altered antigen expression were concerning for therapy-related acute leukemia versus disease progression.  CD138 immunohistochemical stain and kappa light chain in situ hybridization (E and F), was consistent with plasmablastic transformation.