重症筋無力症，全身性エリテマトーデス，関節リウマチを合併した外陰部悪性黒色腫に対してニボルマブ投与と放射線療法が奏功した 1 例

A woman in her 50s had myasthenia gravis (MG), rheumatoid arthritis (RA), and systemic lupus erythematosus (SLE). Enlargement resection and colostomy were performed for malignant anal melanoma (Stage IB T1bN 0 M 0). There was no recurrence during the follow-up period. Three years later, she developed pain and bleeding from the vulva. As an irregular black-colored macule and nodules in the vagina and external urethral meatus were observed separately from the surgical margin, recurrence from eld cells was suspected. We found a large unresectable mass that had directly invaded the urethra and remained in the rectum, and initiated concurrent irradiation and nivolumab treatment. After the 15th administration of nivolumab and 45 Gy of irradiation, the tumor had markedly decreased in size without any new metastatic lesions. The antitumor mechanism is considered to be via abscopal and synergistic effects, as demonstrated by increased PD-L1 expression. However, there are few case reports of combination therapy of nivolumab and radiotherapy for malignant melanoma in Japan.