Antigenic phenotypes of hairy cell leukemia and monocytoid B-cell lymphoma: an immunohistochemical evaluation of 66 cases.

Using a large panel of antibodies on multi-tumor block sections of routinely processed, paraffin-embedded fixed tissue, we compared the antigenic phenotype of 42 clinically, morphologically, and immunologically well-characterized cases of hairy cell leukemia (HCL) with 24 cases of monocytoid B-cell lymphoma (MBCL) selected from the Monocytoid B-Cell Lymphoma Registry at the City of Hope National Medical Center. The predominant antigenic phenotype of hairy cells was CD45 (leukocyte common antigen)+, CD45Ra (4KB5, MB1, MT2)+, L26+, CDw75 (LN1)+, CD74 (LN2)+, LN3+, MB2+, CD45RO (UCHL1)-, MT1-, CD15 (Leu-M1)-, neuron-specific enolase (NSE)-, epithelial membrane antigen-, and CD30 (Ber-H2)-. The immunophenotype of neoplastic monocytoid B lymphocytes was essentially identical to that of the hairy cells, with one exception: the neoplastic monocytoid B lymphocytes were stained by epithelial membrane antigen in seven cases. An interesting observation was the staining by anti-muscle-specific actin of the neoplastic cells of MBCL in 53% of cases, but of none of the cases of HCL. The results of our study (1) indicate that HCL and MBCL can be immunophenotyped reliably on fixed tissue samples, (2) further confirm the proposed lineage relationship between these two lymphoproliferative disorders, and (3) indicate that decalcification of bone marrow biopsies does not adversely affect the immunoreactivity of hematopoietic-associated antigens.