Concomitant Presence of CD5-Positive Diffuse Large B-Cell Lymphoma and Monoclonal B Cells with the “CLL Immunophenotype” - Is It Richter’s Transformation?

The presence of diffuse large B-cell lymphoma (DLBCL) with a concomitant unsuspected population of B cells with chronic lymphoid leukemia (CLL) phenotype is very rare with no antecedent history of CLL. This may represent cases of de novo Richter’s transformation or the coexistence of two neoplasms [1]. In cases where the monoclonal B-cell population does not exceed 5x109/L, this may represent DLBCL with concomitant monoclonal B-cell lymphocytosis (MBL) of the CLL phenotype. The coexistence of MBL of the CLL phenotype creates a diagnostic conundrum, especially in an unusual case of CD5+ DLBCL as it may be a de novo CD5+ DLBCL or Richter transformation [2]. The former has an aggressive course compared to de novo DLBCLs [3,4]. CLL has been known to occur synchronously or metachronously with hairy cell leukemia [5] and DLBCL [6]. We present here a case of clinically aggressive de novo CD5+ DLBCL with an unsuspected second population of CLL-like MBL detected on flow cytometry.