CD 5

CD5 is expressed normally on all T cells (one of the pan T-cell antigens). It can be aberrantly expressed by B-cell lymphomas (most commonly mantle cell lymphoma, B-cell small lymphocytic lymphoma). Expression of CD5 is useful to support T-cell lineage in T-cell lymphomas, or to help subclassify B-cell lymphomas. CD5-posiitve B-cell lymphomas are heterogenous group of neoplasms. Classification of this group of lymphomas has important clinical and prognostic significance. CD5-positive B-cell lymphomas consist primarily of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) and mantle cell lymphoma (MCL). However, CD5 expression has been reported in a number of other B-cell lymphomas. We report the clinical, morphologic, immunophenotypic and molecular genetics features of several series of CD5-positive B-cell lymphomas that lack the prototypic characters of CLL/SLL or MCL, including follicular lymphoma, MALT lymphoma, nodal marginal zone lymphoma and lymphoplasmacytic lymphoma. Our results show that CD5 expression is often associated with an increased tendency of disseminated disease in MALT lymphoma and nodal marginal zone lymphoma, but these patients usually have an indolent clinical course and excellent overall survival with appropriate management. However, in follicular lymphoma, CD5 expression is associated with a higher International Prognostic Index, higher rate of transformation to diffuse large B-cell lymphoma and shorter progression-free survival. We summarize that CD5 expression not only produces diagnostic challenges in the classification of CD5-positive B-cell lymphomas but also bears prognostic significance.