Although photodynamic therapy (PDT) is an effective treatment option for non-melanoma skin cancer, the development of aggressive tumours in PDT-treated areas has been described. To evaluate the clinical, histological, and biological characteristics of squamous cell carcinomas (SCCs) in areas previously treated with PDT vs those arising in areas never treated with this therapeutic modality. A retrospective observational study was designed. We collected all cases of invasive SCCs in areas previously treated with PDT. The control group consisted of an equivalent number of SCCs randomly selected from the database of our pathology department. Expression of specific markers implicated in SCC progression, including p53, Ki67, COX-2, cyclin D1, E-cadherin, EGFR, survivin, and pERK, was analysed. A total of 699 patients were treated with PDT for non-melanoma skin cancer during the course of the study. Ten invasive SCCs arising in areas previously treated with methylaminolevulinate-PDT were diagnosed in six patients. The control group consisted of 10 invasive SCCs from 10 patients never treated with PDT. In the PDT group, the mean tumour size was significantly lower and the absence of ulceration was more frequent than in the control group (p<0.024 and p = 0.035, respectively). A diffuse survivin staining pattern was observed in 90% of tumours in the PDT group versus 50% in the comparative group (p = 0.141). The number of SCCs arising in areas previously treated with PDT was very low and did not differ significantly from that of SCCs developing in non-PDT-treated areas.
Keywords: COX-2; E-cadherin; EGFR; Ki67; cyclin D1; non-melanoma skin cancer; p53; pERK; photodynamic therapy; squamous cell carcinomas; survivin.