Acral lentiginous melanoma treated with topical imiquimod cream: possible cooperation between drug and tumour cells.

An 85-year-old woman presented with a lesion on the sole of her right foot, which was histologically confirmed as acral lentiginous melanoma. Because of the large field involved and because the patient refused any invasive or painful treatment, topical treatment with imiquimod was commenced. At the 20-month follow-up, the patient was still continuing treatment with topical imiquimod, and no metastases to the lymph nodes or viscera were found, either clinically or in imaging studies. We believe that the success of the treatment cannot be explained only by the stimulation of the immune system induced by imiquimod. A possible explanation might be 'tumour dormancy', where a tumour grows very slowly because of a balance between the neoplasia and the immune (and nonimmune) mechanisms of tumour control. The use of imiquimod has so far allowed our patient to avoid surgery, and perturbation of the mechanisms of tumour regulation, such as local immunity and angiogenesis, has not taken place.