Eruptive epidermoid cysts resulting from treatment with imiquimod.

Background: Because of its unique mechanism of action and safety profile, imiquimod, a topical immune response modifier, is used for many benign and malignant dermatologic conditions. Adverse effects are typically limited to treatment site erythema and erosion.

Objective: To describe a newly recognized adverse effect of imiquimod.

Methods: A 79-year-old woman being treated with imiquimod 5 days per week for a nodular basal cell developed a verrucous plaque over the treatment area after 7 weeks of therapy.

Results: Scouting biopsies demonstrated multiple comedones and ruptured epidermoid cysts. There was no evidence of residual basal cell carcinoma.

Conclusions: Imiquimod is a new and novel treatment option for cutaneous malignancies. We report its successful use in the treatment of a nodular basal cell carcinoma. The multiple comedones and ruptured epidermoid cysts are newly reported adverse effects of imiquimod therapy.