Marginal zone variant of mantle cell lymphoma: CD5-negative cyclin D1-positive variant posing a diagnostic dilemma.

Described herein is an unusual case of mantle cell lymphoma (MCL) histologically mimicking marginal zone lymphoma (MZL). An 83-year-old man presented with multiple adenopathies and a hilar mass encroaching on the right lung. A transbronchial biopsy showed small blue cells suspicious for small cell carcinoma. On further analysis the cells were predominantly small cleaved and CD20 positive, suggesting follicular lymphoma, grade 2. An axillary lymph node biopsy showed germinal centers surrounded by monocytoid B cells. Flow cytometry was negative for CD5 and CD23 and the diagnosis of MZL was considered. Because of the aggressive clinical behavior, including extensive necrosis on imaging studies, immunohistochemistry for cyclin D-1 was performed and was positive. Bone marrow was extensively involved and it showed t(11;14), in addition to other complex cytogenetic abnormalities. Differentiating MCL from MZL has prognostic and therapeutic implications, particularly when considering the potential role of targeted therapy and cell cycle modulators.