KSHV- and EBV-associated germinotropic lymphoproliferative disorder.

Kaposi sarcoma-associated herpesvirus (KSHV) is known to be associated with 3 distinct lymphoproliferative disorders: primary effusion lymphoma (PEL), multicentric Castleman disease (MCD), and MCD-associated plasmablastic lymphoma. We report 3 cases of a previously undescribed KSHV-associated lymphoproliferative disorder. The disease presented as localized lymphadenopathy and showed a favorable response to chemotherapy or radiotherapy. Histologically, the lymphoproliferation is characterized by plasmablasts that preferentially involved germinal centers of the lymphoid follicles, forming confluent aggregates. They were negative for CD20, CD27, CD79a, CD138, BCL6, and CD10 but showed monotypic kappa or lambda light chain. Clusters of CD10(+)CD20(+) residual follicle center cells were identified in some of the follicles. The plasmablasts were positive for both KSHV and EBV, and most of them also expressed viral interleukin-6 (vIL-6). Unexpectedly, molecular analysis of whole tissue sections or microdissected KSHV-positive aggregates demonstrated a polyclonal or oligoclonal pattern of immunoglobulin (Ig) gene rearrangement. The plasmablasts showed somatic mutation and intraclonal variation in the rearranged Ig genes, and one case expressed switched Ig heavy chain (IgA), suggesting that they originated from germinal center B cells. We propose calling this distinctive entity "KSHV-associated germinotropic lymphoproliferative disorder."