Axillary Lymph Node Malignant Melanoma of Unknown Primary Origin: A Case Report From Japan

Malignant melanoma of unknown primary origin (MUP) is a rare disease predominantly reported in Caucasian individuals. In this paper, we report a rare case of MUP. We treated a 75-year-old Japanese man with an MUP localized to the axillary lymph nodes. The primary tumor could not be identified despite available investigations. We performed radical lymph node dissection and administered postoperative adjuvant therapy using the molecular-targeted drugs dabrafenib and trametinib. Ten months after surgery, the patient experienced a favorable clinical course with no recurrence or complications from surgery or medication. The frequency and clinical characteristics of malignant melanoma differ among ethnic groups, and very few reports of MUP have been documented in East Asia.