Primary cutaneous CD5+ marginal zone B‐cell lymphoma resembling the plasma cell variant of Castleman's disease

Marginal zone B-cell lymphoma (MZBL) is occasionally associated with prominent plasma cell differentiation. However, MZBL rarely exhibits histological features that resemble plasmacytoma arising from a localized plasma cell variant of Castleman's disease (PCCD). We here report a histologically similar case that was associated with primary cutaneous tumor. The patient was a 57-year-old woman with a 5-year history of cutaneous nodules. Histologically, a prominent proliferation of plasma cells occupied the interfollicular area of the central portion of the cutaneous tumor, whereas various numbers of CD5+ centrocyte-like (CCL) cells, which were arranged in a marginal zone distribution pattern, occupied the peripheral region of the tumor. The majority of the lymphoid follicles had atrophic or regressive germinal centers resembling hyaline-vascular Castleman's disease. CCL cells were observed to have colonized a few of the lymphoid follicles. Immunohistochemistry revealed that these cells had a monotypic intracytoplasmic kappa chain. Without treatment, the patient was quiescent, but 2 years later, there was a transformation to the large cell type. These observations suggest that MZBL needs to be distinguished from PCCD, and that untreated cutaneous MZBL may undergo a high-grade blastic transformation similar to other indolent lymphoproliferative disorders.