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Primary cutaneous follicle center lymphoma (PCFCL) is the most common cutaneous B-cell lymphoma. The typical immunophenotype includes expression of both CD20 and BCL6, with the majority of cases lacking expression of CD10, BCL2, and the characteristic t(14;18)/IGH-BCL2 rearrangement seen in systemic follicular lymphoma (FL). Plasmacytic differentiation (PD) is an uncommon finding in both systemic and cutaneous FLs and presents a diagnostic challenge when present, leading to the potential for misdiagnosis as marginal zone lymphoma (MZL). Limited reports have described light chain restriction in the plasma cell component of FLs with PD, and rare cases of PCFCL with PD have been described. While the IGH-BCL2 translocation has been identified in a subset of FLs with PD, the presence of the BCL2 translocation in monotypic plasma cells of PCFCL has not been previously described to our knowledge. Here, we report a case of PCFCL with extensive PD in a 77-year-old woman that was favored to represent primary cutaneous MZL on an initial punch biopsy. Excisional biopsy, however, revealed that the atypical lymphocytes expressed CD10, BCL6, and BCL2, while the plasma cell component demonstrated light-chain lambda restriction. FISH studies showed the presence of an IGH-BCL2 translocation in both the lymphocytic and plasmacytic components., (© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Follicle center lymphomas, including primary cutaneous follicle center lymphoma (PCFCL), may rarely show plasmacytic differentiation. Such cases can pose a diagnostic challenge and can be mistaken for other lymphomas that more commonly include plasma cells. Here, we report four cases of PCFCL and one case of systemic follicular lymphoma involving the skin with associated monotypic plasma cells, including the clinical, morphologic and immunophenotypic features., (© 2020 John Wiley & Sons A/S . Published by John Wiley & Sons Ltd.)