CD5^- small B-cell leukemias are rarely classifiable as chronic lymphocytic leukemia

Expression of the CD5 antigen by neoplastic cells often is considered a diagnostic criterion for B-cell chronic lymphocytic leukemia (B-CLL). However, published series frequently include a number of CD5^-cases. We studied the spectrum of CD5^- B-cell lymphoproliferative disorders presenting with leukemic involvement and reassessed the prevalence of CD5^- BCLL. We immunophenotyped 192 cases of clonal, small lymphocytic, B-cell disorders involving peripheral blood or bone marrow. Of these, 41 CD5^- cases were further analyzed, correlating the immunophenotypic findings with pathologic material and clinical data. Only 3 CD5^- cases were classified as CD5^- B- CLL. These 3 cases had features unusual for B-CLL, including bright surface immunoglobulin expression, bright CD20 expression, and absence of CD23 expression (2 cases) or Richter syndrome (1 case). The remainder of the CD5^- cases consisted of hairy cell leukemia, hairy cell variant, prolymphocytic leukemia, follicular center cell lymphoma, lymphoplasmacytic lymphoma, splenic marginal zone lymphoma (SMZL), small lymphocytic lymphoma with marrow fibrosis, and lymphoma, not further classified. Eight cases remained unclassified, but some displayed features of SMZL. CD5^- lymphoproliferative disorders of peripheral blood or bone marrow are unlikely to be CLL and often are classified more appropriately as non-Hodgkin lymphoma in the leukemic phase.