CD5 Negative Mantle Cell Lymphoma with MYC Protein Expression by Immunohistochemistry

Summary: Mantle cell lymphoma (MCL) is an uncommon B-cell lymphoma that rarely involves the skin. Cutaneous MCL almost always presents in the setting of disseminated disease and is associated with a poor prognosis. We present a case of an 82 year old woman who presented with multiple plaques and nodules on the trunk, extremities, and scalp. Two lesions from the right arm were biopsied. The clinical differential diagnosis included mycosis fungoides, Sweet syndrome, and Merkel cell carcinoma. Histologic sections demonstrated a diffuse dermal infiltrate of monomorphous mononuclear cells with high nuclear to cytoplasmic ratio, open chromatin, and crush artifact. The cells were positive for CD20, Cyclin D1, Sox-11, BCL-2, and MYC by immunohistochemistry. The Ki-67 proliferative index was close to 100%. Additional clinical correlation revealed that the patient had a history of mantle cell lymphoma. Given the clinical history, morphology, and immunophenotype, a diagnosis of mantle cell lymphoma, blastoid variant, was rendered. Recently, MYC gene rearrangements have been described in mantle cell lymphoma and portend a poor prognosis. Studies have shown that assessment of MYC protein expression by immunohistochemistry is predictive of clinical outcome. This unusual case demonstrates the importance of maintaining a high index of suspicion for mantle cell lymphoma despite the lack of CD5 expression and also emphasizes the importance of assessing MYC protein expression in cases of mantle cell lymphoma.