The
CD5 antigen is a T-cell associated marker that is also usually expressed by two B-cell
neoplasms,
chronic lymphocytic leukemia/
small lymphocytic lymphoma and
mantle cell lymphoma. We observed
CD5 antigen expression in a subset of cases of intravascular large
B-cell lymphoma (IVLBL), and we report here five cases. The patients, two men and three women, ranged in age from 59 to 81 years. Biopsy specimens were obtained from kidney, lung, bone marrow, abdominal wall, and neck, the latter involving a
lymphangioma. All of the cases had histologic features typical of IVLBL, with large and atypical lymphoid cells located predominantly within blood vessels. Immunohistochemical studies performed using routinely fixed,
paraffin-embedded tissue sections showed that the neoplastic cells were B cells, positive for the
CD20 antigen and negative for the CD3 or
CD43 antigens. All cases were also positive for the
CD5 antigen. One case had an
immunoglobulin heavy chain gene rearrangement shown by using a polymerase chain reaction method. The finding of
CD5 antigen expression in a subset of IVLBL cases adds to other evidence in the literature suggesting that IVLBL is a heterogeneous entity. We considered the possibility that these cases were related to or represented unusual histologic forms of transformation from either
chronic lymphocytic leukemia/
small lymphocytic lymphoma or
mantle cell lymphoma. All of the cases, however, were negative for the
CD23 antigen and
cyclin D1 (bcl-1)
protein, which is evidence against this interpretation. The
biologic significance of
CD5 antigen expression in cases of IVLBL is uncertain. These
neoplasms might arise from a separate lineage of CD5-positive B cells or from a specific, early stage of B-cell differentiation. Alternatively, some investigators have suggested that
CD5 antigen expression by B cells is a marker of activation.