Multiple myeloma with hairy cell-like features.

Hairy cell leukemia (HCL) and multiple myeloma (MM) are well-described disease entities with characteristic clinical and pathologic features. We describe two patients initially treated for MM in whom atypical clinical and morphologic features subsequently developed that raised the possibility of HCL. Although the cytologic appearance and immunophenotype were not diagnostic of HCL, these cases challenge the criteria used to diagnose MM, HCL, and other recently described villous neoplasms.

CD20 (pan-B cell antigen) expression on bone marrow-derived T cells.

Antibodies directed against CD20 (L26, Leu 16, and B1) are frequently used to determine the presence of B lymphocytes. However, recent publications describe the unexpected presence of CD20-positive T cells in the peripheral blood of normal subjects and occasional T-cell neoplasms that express CD20. To determine the presence of CD20-positive T cells in bone marrow, flow cytometric analysis was performed on 34 aspirate specimens (14 normal, 5 acute lymphoblastic lymphoma [ALL], 5 acute myelogenous leukemia [AML], 4 HIV positive, 2 myelodysplastic/myeloproliferative, 2 chronic myelogenous leukemia [CML], 1 chronic lymphocytic lymphoma [CLL], 1 multiple myeloma). A small population of cells coexpressing CD3 (Leu 4) and CD20dim (Leu 16) was identified in 94% of the specimens, representing 0% to 11% (mean 1.77%) of marrow mononuclear cells and 0% to 22.2% (mean 6.54%) of marrow lymphoid cells. There was no correlation between the percentage of CD20-positive T cells and the CD4:CD8 ratio, patient age, gender, or diagnosis. CD20dim positive cells included immature B cells and CD20-positive T cells. Although evaluation of CD20 expression is useful in delineating B-cell processes, caution should be exercised in interpreting its expression on bone marrow T-lymphoid cells. CD20 expression on T cells may be seen in either normal, reactive, or neoplastic processes.