Paucity of intraepidermal FoxP3‐positive T cells in cutaneous T‐cell lymphoma in contrast with spongiotic and lichenoid dermatitis

Abstract

Background: FoxP3 is the most specific available marker for regulatory T cells (Tregs). Tumor‐associated FoxP3‐positive Tregs have been identified in various neoplasms, including cutaneous T‐cell lymphoma (CTCL). FoxP3 expression in CTCL varies across groups; few studies have compared CTCL with inflammatory conditions. Methods: Lesional skin biopsies from 20 patients with CTCL [13 mycosis fungoides (MF); 7 Sézary syndrome (SS)] and 22 with inflammatory dermatoses (11 spongiotic; 11 lichenoid or interface) were examined for FoxP3 expression by immunohistochemistry. Epidermal FoxP3‐positive lymphocytes were counted as a percentage of the total epidermal CD3‐positive T‐cell population. Results: FoxP3‐positive T cells composed the minority of infiltrate in all major categories. Lower numbers of epidermal FoxP3‐positive T cells were observed in CTCL, particularly MF, than in inflammatory dermatoses (P < .001). CTCL neoplastic T cells did not express FoxP3. Conclusion: FoxP3‐positive T cells are less frequently encountered in MF than in inflammatory dermatoses. FoxP3‐positive T cells occur in higher proportions in the dermis than in the epidermis and probably correlate with coexisting inflammatory components. CTCL neoplastic cells do not typically express a Treg phenotype and are associated with low numbers of FoxP3‐positive Tregs in the infiltrate. FoxP3 expression by immunohistochemistry may aid histologic evaluation of these conditions. Wada DA, Wilcox RA, Weenig RH, Gibson LE. Paucity of intraepidermal FoxP3‐positive T cells in cutaneous T‐cell lymphoma in contrast with spongiotic and lichenoid dermatitis.