FoxP3-Positive Cells and Their Contacts with Mast Cells Are Highly Increased in Basal Cell Carcinoma

Introduction: The cells of the immune system are thought to contribute to the development of skin cancers, such as basal cell carcinoma (BCC). One possible mechanism may be the interaction between mast cells and regulatory T cells (Tregs), resulting in immunosuppression. Methods: Fresh-frozen biopsies from the lesional and nonlesional skin of 16 patients with BCC were processed for the enzymehistochemical staining of mast cell tryptase, immunohistochemical staining of FoxP3 (a marker of Tregs) as well as for the double-staining method to label tryptase(+) cells and FoxP3(+) cells on the same cryosection. The cell numbers and apparent morphological contacts (AMCs) between these cell types were counted. Results: There was a high increase in the number of tryptase(+) cells, FoxP3(+) cells, and AMCs between them in the lesional compared to corresponding nonlesional skin (p < 0.0001) in all cases. Conclusion: A morphological basis is theoretically present in BCC, suggesting an immune evasive microenvironment.