Atypical pseudoepitheliomatous hyperplasia and squamous cell carcinoma in chronic cutaneous sinuses and fistulas.

Three cases are presented in which changes of atypical pseudoepitheliomatous hyperplasia (APH) occurred in chronically draining cutaneous sinuses and fistulas. In two of the cases, unequivocal squamous cell carcinoma developed. Because the term APH fails to convey adequately to the surgeon the essentially malignant nature of this process and the need for aggressive treatment, we feel that the term should be discarded. Based on our cases and those reported in the literature, it is our opinion that, in the presence of soft-tissue and bony invasion, a diagnosis of well-differentiated squamous cell carcinoma is appropriate even in the absence of unequivocal cellular changes of malignancy.