Apparent progression of lentigo maligna to invasive melanoma during treatment with topical azelaic acid.

Nine patients with lentigo maligna were treated with topical azelaic acid. Clinical improvement was observed in four, with complete clearing in one. Two patients developed invasive lentigo maligna melanoma while on treatment. Caution should be exercised in the use of topical azelaic acid in the treatment of lentigo maligna.