Marked response to imatinib mesylate in metastatic acral lentiginous melanoma on the thumb.

We report a case of melanoma that had a marked response to treatment with imatinib mesylate (IM). The patient was a 61-year-old man who presented with a small red nodule on the thumb and destruction of the nail plate. On histological examination, this lesion was diagnosed as a melanoma, and computed tomography revealed lymph-node swelling in the left axilla and nodules in both lung fields. Although the patient received intratumoral injections of interferon-β and systemic administration of dacarbazine, both primary and metastatic lesions increased in size. Immunochemistry detected a KIT mutation, which was confirmed by DNA sequencing analysis, and patient was given IM. Within 2 weeks of starting the IM regimen, the size of the nodule on the nail plate markedly decreased, and the axillary lymph-node swelling and lung-nodule formation regressed. This case suggests that IM may be a promising treatment option for KIT mutation-positive melanoma.