Treatment of lentigo maligna (melanoma in situ) with the immune response modifier imiquimod.

Background: Surgical excision is the treatment of choice for lentigo maligna (LM), or melanoma in situ. Topical application of imiquimod, a local immune response modifier, is a novel therapeutic approach that leads to LM tumor clearance. This pilot, open-label, nonrandomized study evaluates the efficacy of imiquimod in patients with LM and other systemic problems that make them poor surgical risks.
Observations: Six biopsy-proven cases of LM from 5 patients (age range, 67-80 years) in whom standard surgical therapy was contraindicated were enrolled in the study. Five tumors were located on the face and 1 on the right shoulder. Imiquimod was used as a 5% cream once a day for a maximum of 13 weeks. Immediate clinical responses and follow-up, as well as histopathologic changes and immunohistologic parameters (in 2 patients), were analyzed. The complete response rate for all LM cases was 100%. Time to complete clearing varied from 5 to 13 weeks based on both clinical and histopathologic findings. The inflammatory infiltrate following imiquimod treatment consisted of T-helper lymphocytes mixed with a significant number of cytotoxic cells and monocytes or macrophages. These results indicate that imiquimod induces a cytotoxic T-cell-mediated immune response. In all patients, erythema and erosions occurred at the treated area 2 to 4 weeks after initiation of imiquimod therapy. The patients have been followed up for 3 to 18 months without evidence of recurrences.
Conclusions: Topical imiquimod appears to be an excellent therapeutic option for LM. Close evaluation of patients, including posttherapy histopathologic investigation, is essential. Imiquimod can be added to the list of therapeutic approaches for carefully selected patients with LM.