CD5+ B-cell lymphoproliferative disorders: Beyond chronic lymphocytic leukemia and mantle cell lymphoma.

CD5 positivity in B-cell lymphoproliferative disorders (LPD) is usually considered characteristic of either chronic lymphocytic leukemia (CLL) or mantle cell lymphoma (MCL). However, other neoplastic B-LPDs may express CD5, albeit infrequently. In this study we have reviewed the tissue pathology of CD5+ B-LPDs that do not fulfill diagnostic criteria for CLL or MCL on flow cytometric studies of peripheral blood or bone marrow. Our results indicate that although CD5 positivity is most commonly associated with CLL and MCL, a significant minority of cases do not fall into these two categories. Phenotypically unusual CLL, marginal zone lymphoma and lymphoplasmacytic lymphoma were the most common diagnoses in this group of patients. Applying strict flow cytometry criteria, using genetic studies, and deferring to a lymph node/tissue diagnosis in non-classical cases are critical for accurate diagnosis and classification of CD5+ B-cell LPD.