Primary CD20+CD10+CD8+ T-cell lymphoma of the skin with IgH and TCR beta gene rearrangement.

Most cutaneous T-cell lymphomas are derived from mature postthymic T cells of the CD4 subtype. When other less common profiles are encountered, a diagnostic challenge is posed. Accurate categorization is critical because of the specificity of therapeutic regimens, including biologics. A 65-year-old woman was seen in 2001 because of a thigh mass manifesting an unusual phenotype eventually categorized as a mature postthymic CD8+ T-cell lymphoma with CD10 and weak CD20 expression. Molecular studies revealed T-cell receptor and heavy chain immunoglobulin rearrangement. Her cutaneous disease progressed despite several cycles of chemotherapy and radiation therapy. However, a therapeutic trial with denileukin diftitox resulted in a striking response. The importance of this case lies in the novel phenotype and dual T- and B-cell rearrangements. Rather than representing an aberrant phenotype, this tumor may represent the malignant counterpart of a benign population of weakly CD20+ T cells of the CD8 subset.