Peculiar clinical and dermoscopic remission pattern following imiquimod therapy of basal cell carcinoma in seborrhoeic areas of the face.

Imiquimod is a 240.3-Da synthetic imidazoquinolinamine (C14H16N4), developed in 1983 and approved in 1997 by the US Food and Drug Administration for the topical treatment of external genital and perianal warts and, more recently, also for actinic keratosis and superficial basal cell carcinomas. We report five cases of patients affected by basal cell carcinomas localized in seborrhoeic areas of the face, successfully treated with topical imiquimod and characterized by the occurrence of eruptive epidermoid cysts at the end-point of therapy. The dermatoscopic evaluation disclosed the presence in all lesions of a common feature characterized by a hyperkeratotic yellow-withish area, resembling 'popcorn', excluding dermoscopic basal cell carcinoma features. Furthermore, histological proof confirmed the diagnosis of epidermoid cysts. As reported in the literature and as observed in our clinical experience, the occurrence of epidermoid cysts, after the topical treatment of basal cell carcinomas with imiquimod, may represent a local immune reaction that is drug-related and is a typical remission pattern in particular anatomical areas. We also emphasized the usefulness of dermoscopy in supporting the clinical diagnosis of epidermoid cysts, excluding the presence of tumoural residue or recurrence. In the future, it will be possible to follow-up the lesions after treatment avoiding the post-control biopsy punch.