The utility of B-cell receptor gene rearrangement studies in diagnosing diffuse large B-cell lymphoma with plasmacytic differentiation.

We present the case of a 50-year-old man with nodal diffuse large B-cell lymphoma characterized by CD10, BCL-6, and BCL-2 expression and a complex karyotype, including t(14;18)(q32;q21) and del6q, suggesting transformation from an antecedent follicular lymphoma. Following rituximab-based chemotherapy, residual nodal disease was characterized by a proliferation of plasmacytoid cells positive for CD138, MUM-1, and cytoplasmic kappa light chain. Immunoglobulin heavy chain and kappa light chain gene rearrangement studies detected the same clone in the diagnostic and post-therapy lymph node specimens. This case illustrates the diagnostic utility of B-cell receptor gene rearrangement studies in detecting a clonal relationship in lymphoma cases with extensive morphologic and immunophenotypic variation following chemotherapy.