Value of CD23 determination by flow cytometry in differentiating mantle cell lymphoma from chronic lymphocytic leukemia/small lymphocytic lymphoma

Mantle cell lymphoma (MCL) and chronic lymphocytic leukemia/small lymphocyt ic lymphoma (CLL/SLL) share many morphologic and immunophenotypic features. In addition to histomorphologic examination, it is customary to use the ab sence of CD23 to differentiate MCL from CLL/SLL, based primarily on reporte d comparisons of immunohistochemical staining of tissue sections. These fin dings are widely extrapolated to flow cytometric analysis, although availab le data are contradictory and not sufficiently detailed. We compared expres sion of CD23 by flow cytometry in 22 cases of MCL and 25 cases of CLL/SLL. Lymphoma cells in 12 of 22 MCLs were negative for CD23, and 10 showed dim e xpression. In contrast, none of 25 CLL/SLLs were negative for CD23, 4 were dimly positive, and 21 were moderately or brightly positive. Thus, a signif icant proportion of MCL exhibited overlap of CD23 expression in the low-int ensity range with CLL/SLL. Clinically. there was no correlation between the intensity of CD23 expression and clinical stage at diagnosis or survival. These findings emphasize that by flow cytometry, MCL can be differentiated reliably from CLL/SLL using CD23 if negative expression is observed However , with dimly positive expression, interpretation should be cautious.