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Case ReportsAbstract
Primary cutaneous follicle center lymphoma (PCFCL) is a germinal center-derived B-cell lymphoma representing approximately 10% of primary cutaneous lymphomas. Patients often present with nodules or plaques on the head or trunk composed predominantly of medium to large lymphocytes arranged in a follicular or diffuse growth pattern. When diffuse large cell proliferation is observed, differential diagnoses should include primary cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL-LT) and secondary cutaneous lymphomas. This case study underscores the diagnostic challenges of distinguishing these entities when morphologic and phenotypic overlap occurs, necessitating additional studies. A 66-year-old male with a history of lentigo maligna and Bowen’s disease presented with erythematous, scaling papules on his scalp and a violaceous papule on his temple. Microscopic examination of both sites revealed diffuse sheets of large lymphocytes with enlarged nuclei and vesicular chromatin infiltrating the dermis, sparing the epidermis. These cells stained positive for CD20, PAX-5, CD10, and BCL6, but negative for BCL2, MUM1, and FOXP1. The Ki-67 index was 60%. An EBV stain was negative. The high Ki-67 and quantity of large cells in this case raised some concerns, especially since expression of CD10 is uncommon in diffuse PCFCL, making it crucial to first exclude other entities. However, PCDLBCL-LT and nodal follicular lymphomas commonly express BCL2, along with MUM1 and FOXP1 in PCDLBCL-LT. Negative FISH results for MYC, BCL2, and BCL6 rearrangements, combined with lack of extracutaneous involvement through bone marrow biopsy, flow cytometry analysis, and PET/CT scans, support a diagnosis of PCFCL, large cell variant.