Mycosis fungoides with CD20 expression: report of two cases and review of the literature.

CD20 expression is exceedingly rare in T-cell lymphomas. Most published cases have been diagnosed as peripheral T-cell lymphomas, not otherwise specified. Only 18 cases of CD20-positive mycosis fungoides (MF) have been previously reported. Here, we describe two cases of CD20-positive MF. Patient 1 was an 84-year-old woman who presented with a 5-year history of multiple pruritic erythematous papules coalescing into thin plaques over 80% of her body surface area. She expired after developing tumors and large cell transformation. Patient 2 was a 67-year-old woman with a long-standing history of tumor stage MF with large cell transformation. She developed a nodular plaque while receiving topical and systemic therapy. In both cases, the neoplastic T-cells demonstrated a CD4-positive immunophenotype with loss of pan-T-cell markers and a monoclonal T-cell receptor gamma gene rearrangement. CD20 was expressed by a significant population of the neoplastic T-cells, but these T-cells lacked expression of other B-cell markers, including CD79a, CD19 and PAX5. This report adds to and summarizes the small body of literature describing CD20-positive MF, and discusses diagnostic and clinical implications.