FoxP3-positive cells and their contacts with mast cells are highly increased in basal cell carcinoma

The cells of the immune system are thought to contribute to the development of skin cancers through immune evasion. One possible mechanism for this can be the interaction between mast cells and regulatory T cells (Tregs). Therefore, fresh frozen biopsies from the lesional and nonlesional skin of 16 patients with basal cell carcinoma (BCC) were processed for the enzymehistochemical staining of mast cell tryptase, immunohistochemical staining of FoxP3 as well as for the double-staining method to label tryptase + cells and FoxP3 + (a marker of Tregs) cells on the same cryosection. The cell numbers and apparent morphological contacts (AMCs) between these cell types were counted. The results show 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). Therefore, a theoretical morphological basis is present in the BCC lesion for permitting an immune evasive microenvironment.