Topical photodynamic therapy significantly reduces epidermal Langerhans cells during clinical treatment of basal cell carcinoma

Background Topical photodynamic therapy (PDT) is a widely applied treatment for basal cell carcinoma (BCC). PDT-induced immunosuppression leading to reduced antitumour immune responses may be a factor in treatment failure. Objectives To examine the impact of topical PDT on leucocyte trafficking following clinical treatment of BCC. Methods Superficial BCCs in eight white caucasian patients were treated with methyl aminolaevulinate (MAL)-PDT. Biopsies for immunohistochemical assessment were taken from BCCs pre-PDT, 1 h and 24 h post-PDT and from untreated healthy skin. Results Treatment of BCC with MAL-PDT produced a rapid neutrophil infiltration, commencing by 1 h and significantly increased at 24 h post-PDT (P < 0.05 compared with baseline). An associated increase in the number of blood vessels expressing E-selectin was observed at 1 h and 24 h post-PDT (both P < 0.05 compared with baseline). In contrast, the number of epidermal Langerhans cells fell sharply by 1 h post-PDT, and remained significantly reduced at 24 h post-PDT (both P < 0 05 compared with baseline). Conclusions Reduction of Langerhans cells during clinical treatment of BCC might potentially impact negatively on antitumour responses through reduced activation of tumour-specific effector cells. Investigation of modified PDT protocols with the aim to minimize immunosuppressive effects while maintaining antitumour efficacy is warranted.