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Case Reports

Abstract

Mantle cell lymphoma (MCL) is a rare, aggressive form of non-Hodgkin's lymphoma. Cutaneous MCL is rare, almost always associated with systemic disease, and most commonly represents relapse or progression. We present a case of cutaneous MCL that clinically and histologically mimicked primary cutaneous diffuse large B-cell lymphoma, leg type (pcDLBCL-lt). A 76-year-old male presented to an outside dermatology clinic with a large friable nodule on the pretibial leg. The clinician’s differential diagnosis was pcDLBCL-lt, Merkel cell carcinoma or melanoma. Histopathology showed a dense dermal infiltrate of mostly intermediate sized atypical lymphocytes which were positive for CD20, bcl2, and Mum-1 and negative for CD3, CD10, and CD30. A diagnosis of pcDLBCL-lt was considered given the immunophenotype, clinician’s impression, and clinical presentation. However, further immunohistochemical evaluation was performed due to the monomorphic cytology, which showed the infiltrate to be positive for cyclin D1, CD5 and SOX11, compatible with MCL. Upon further clinical investigation, the patient was confirmed to have systemic mantle cell lymphoma. This case highlights a potential pitfall in the histopathologic diagnosis of MCL metastatic to the skin when presenting on the lower extremity, as MCL and pcDLBCL-lt may have overlapping cytologic features, especially the blastoid and pleomorphic subtypes, and immunohistochemistry profiles are both positive for Bcl2 and Mum-1. CD5 and SOX11 are helpful to distinguish the two entities as they are typically positive in MCL and negative in DLBCL. Molecular studies identifying the hallmark translocation seen in MCL (t(11;14)(q13;q32)) may also be performed.