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.