CD20+ mycosis fungoides: a report of three cases and review of the literature.

Mycosis fungoides (MF) is the most common of the family of cutaneous T-cell lymphomas, accounting for 65% of all cases of cutaneous T-cell lymphomas. The classic phenotypic profile is one defined by CD4+ T cells showing a reduction in the expression of CD7 and CD62L. There are 3 previous reports describing CD20 expression in MF. The cell surface antigen CD20 is a transmembrane glycosylated phosphoprotein expressed in the early stages of B-cell development before differentiation into plasma cells. Two male patients, aged 14 and 44 years, presented with persistent truncal plaques up to 8 cm of 1 and 4 years duration, respectively. A third patient, an 80-year-old female, presented with a 1-year history of progressive nodules involving the head and neck area. Cases 1 and 2 both responded to topical treatment modalities. The biopsies in cases 1 and 2 showed features typical of plaque stage MF, whereas case 3 was compatible with follicular MF with tumor stage transformation. Phenotypically, the aberrant cell populace demonstrated a CD4+, CD7-, and CD62L- phenotype; at variance with classic MF was the expression of CD20. Although there were a few PAX5-positive staining cells, definitive colocalization studies were negative. Other B-cell markers and heavy chain immunoglobulin rearrangement were not detected. There are a growing number of reports describing T-cell lymphomas and leukemias with CD20 expression. Of the 6 CD20+ MF cases reported in the literature to date, 3 have been associated with a more aggressive clinical course; all but one case have occurred in males.