Primary cutaneous CD20-positive T-cell lymphoma.

CD20 is a transmembrane protein that is expressed by B cells during their development and is, therefore, commonly used to label cells of B lineage in lymphoid infiltrates. CD20-positive T-cell lymphoma is infrequent but well recognized. Cases reported in the literature show a variety of clinical and histoimmunochemical profiles. Primary cutaneous CD20-positive T-cell lymphoma is vanishingly rare; only eight cases have been previously reported. We present two new cases of this entity and describe their clinical, histological and immunohistochemical features. CD20 is a highly specific B-cell marker. However, it has been reported in a subset of normal T-cells in peripheral blood and bone marrow of healthy individuals. This subset of T-cells also expresses more often CD8 and g/d than the CD20-negative T-cells. Two main theories have been postulated to explain the expression of CD20 by neoplastic T-cells. The first possibility is that these lymphomas develop from the CD20-positive subset of normal T-cells. The second theory regards CD20 as an activation marker. Prognostic implications and therapeutic options of T-cell lymphomas with positivity for CD20 remain to be elucidated.