Immunophenotypic characterization of acute leukemia by immunocytology

Immunophenotypic spectrum of plasma cell leukemia

Four cases of plasma cell leukemia (PCL) are reported that illustrate the variable immunotype of this disorder in contrast with the immunologic profile described for normal B-cell maturation and typical multiple myeloma (MM). Mature B-lymphocytes express B1 antigen (Ag) and surface immunoglobulin (SIg) whereas maturation to the plasma cell stage is accompanied by loss of these immunologic markers and expression of T10 Ag, plasma cell Ag (PCA), and cytoplasmic immunoglobulin (CIg). Plasma cells from patients with MM have previously been found to express the immunophenotype of normal plasma cells. In contrast, none of the four cases reported here express an immunologic profile typical for specific B-cell differentiation stages. Only one of four cases was strongly positive for PCA but additionally expressed B1 Ag and SIg. Of the remaining three cases, all expressed T10 Ag and CIg; two cases also expressed SIg, weak PCA, and B1 Ag. All four cases were monoclonal for lambda light chains and negative for common ALL Ag (CALLA). The variable expression of mature B-cell markers and plasma cell markers demonstrates the immunophenotypic spectrum of PCL; the prognostic significance of this heterogeneity needs to be more closely examined.