Failure of extensive extramammary Paget disease of the inguinal area to clear with imiquimod cream, 5%: possible progression to invasive disease during therapy.

BACKGROUND Surgical approaches are the standard treatment for extramammary Paget disease (EMPD), but nonsurgical modalities may be preferred and more appropriate for some patients. Topical administration of imiquimod cream, 5%, has improved or resolved in situ EMPD (n = 21), but treatment failures (n = 6) have also been reported. OBSERVATIONS We treated an elderly patient with initial biopsy-proved in situ genital EMPD with daily topical imiquimod, 5%, for 14 weeks. Midtreatment mapping biopsy specimens demonstrated invasive disease, with minimal clinical improvement. The patient subsequently underwent surgical excision. CONCLUSIONS Of the 27 published cases that describe imiquimod treatment of EMPD, 6 report treatment failure (22%), but factors that may contribute to treatment failure are not well understood. In the present patient, treatment with imiquimod may have been complicated by variable lesion thickness, which inhibited uniform penetration of imiquimod, or the presence of invasive disease not detected on initial biopsy. The efficacy of imiquimod to treat extensive invasive EMPD has not been demonstrated, and surgical approaches remain the most appropriate treatment for invasive disease. Variable responses to topical imiquimod use among patients suggest that other factors may be important in determining response to therapy.