Biclonal light chain gammopathy with aberrant CD33 expression in secondary plasma cell leukemia

Plasma cell leukemia is a rare neoplastic proliferation of circulating plasma cells. Clonal proliferations of plasma cells, such as in plasma cell leukemia or plasma cell myeloma, are typically characterized by production of a monoclonal heavy and/or light chain immunoglobulin. We present a case of a secondary plasma cell leukemia arising from plasma cell myeloma with dual expression of lambda and kappa light chains along with aberrant expression of CD33, CD20, and dim CD56. This case emphasizes the importance of recognizing aberrant immunophenotypes in plasma cell leukemias and represents the first reported case of biclonal light chain expression in a secondary plasma cell leukemia.