Japanese Dermatological Association Guidelines: Clinical Questions of Guidelines for Merkel Cell Carcinoma 2025

Merkel cell carcinoma (MCC) is a highly malignant skin cancer characterized by high rates of recurrence and metastasis. Although rare, the incidence has noticeably increased in recent years. It is also known to be a highly immunogenic tumor, and the use of immune checkpoint inhibitors has begun for advanced cases. However, there had been no guidelines for this disease in Japan. Commissioned by the Japanese Dermatological Association (JDA), this revision was undertaken by a committee comprising experts across relevant fields, who meticulously reviewed and systematized a wide range of literature on MCC to create comprehensive, evidence-based guidelines. Literature searches were conducted by the Japan Medical Library Association. The recommendation statements were determined using the GRADE Grid approach. The guidelines were developed in accordance with the "Minds Clinical Practice Guideline Creation Manual 2020 ver.3.0." Four clinical questions (CQs) were established, and corresponding recommendation statements were provided for each. CQ1 concerns primary tumor resection margins, CQ2 concerns sentinel lymph node biopsy, CQ3 concerns postoperative radiotherapy, and CQ4 concerns chemotherapy for advanced disease. These guidelines are the first of their kind in Japan for MCC, and we hope that they will be useful not only in Japan but also in East Asia, where treatment decisions have previously had to be made based on Western guidelines.