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

Expression of the CD5 antigen by neoplastic cells often is considered a dia gnostic criterion for B-cell chronic lymphocytic leukemia (B-CLL). However; published series frequently include a number of CD5(-) cases. We studied t he spectrum of CD5(-) B-cell lymphoproliferative disorders presenting with leukemic involvement and reassessed the prevalence of CD5; B-CLL. We immuno phenotyped 192 cases of clonal, small lymphocytic, B-cell disorders involvi ng peripheral blood or bone marrow. Of these, 41 CD5(-) cases were further analyzed, correlating the immunophenotypic findings with pathologic materia l and clinical data. Only 3 CD5(-) cases were classified as CD5(-) B-CLL. T hese 3 cases had features unusual for B-CLL, including bright surface immun oglobulin expression, bright CD20 expression, and absence of CD23 expressio n (2 cases) or Richter syndrome (1 case). The remainder of the CD5(-) cases consisted of hairy cell leukemia, hairy cell variant, prolymphocytic leuke mia, follicular center cell lymphoma, lymphoplasmacytic lymphoma, splenic m arginal zone lymphoma (SMZL), small lymphocytic lymphoma with marrow fibros is, 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 cla ssified more appropriately as non-Hodgkin lymphoma in the leukemic phase.