Imiquimod and lentigo maligna: a search for prognostic features in a clinicopathological study with long-term follow-up

Melanoma in situ/lentigo maligna (LM) is a potential precursor of LM melanoma. It occurs most commonly in elderly individuals on sun-exposed skin of the head and neck. Although surgical excision is the treatment of choice, this may not be desirable or feasible for large lesions at functionally or cosmetically important sites. Imiquimod is a topical immunomodulator which can generate a local cytotoxic response with potentially antiviral and antitumour effects. To present our experience of LM treated with imiquimod. A retrospective review was performed of all patients with facial LM treated in our unit with topical imiquimod between January 2001 and December 2006. Pretreatment diagnostic biopsies were also reviewed and histologically graded. Forty-eight patients were treated with imiquimod. There were 37 responders and 11 treatment failures (of whom two were 'partial responders'). Of the 37 responders, 31 showed a clinical inflammatory response to imiquimod. One patient in whom treatment failed subsequently developed invasive disease. The mean follow-up duration was 49 months. We could not identify histological features of prognostic significance. However, the ability to develop an inflammatory reaction to imiquimod was a strong predictor of therapeutic benefit. We consider imiquimod to have a role in the treatment of LM in patients in whom surgery may be contraindicated or for those in whom the cosmetic or functional consequences may be considerable. Until better characterized, its use should probably be confined to centres with experience in the detection and treatment of LM and melanoma.