Background: Malignant melanoma (MM) is a rare but aggressive cutaneous cancer, accounting for only 2% of skin cancers in Japan but nearly half of skin cancer-related deaths. While the global incidence of MM is rising, its epidemiology varies significantly by ethnicity and geographic region. In Japan, melanoma incidence remains lower than in Western countries, with acral lentiginous melanoma (ALM) being the most prevalent subtype. However, comprehensive epidemiological and clinical data remain limited.
Methods: We analyzed data from 7442 Japanese melanoma patients collected between 2005 and 2022 through the Japanese Melanoma Study (JMS). Demographic, clinical, and survival data were evaluated, including subtype distribution, TNM staging, and treatment outcomes.
Results: ALM was the most common subtype (40.8%), followed by superficial spreading melanoma (20.2%). Lymph node metastasis was observed in 28.6% of cases, and distant metastasis in 10.9%. The BRAF mutation rate was 27.2%, with significantly lower frequencies in ALM (8.5%) and mucosal melanoma (4.8%). Among Stage IV patients, those treated with both immune checkpoint inhibitors (ICIs) and BRAF(+ MEK) inhibitors demonstrated significantly improved survival compared to chemotherapy alone (P < 0.05). Adjuvant BRAF(+ MEK) inhibitor therapy also resulted in superior relapse-free survival compared to those who did not receive adjuvant therapy (P < 0.005).
Conclusion: This study provides the largest dataset of Japanese melanoma patients to date, highlighting distinct epidemiological and clinical characteristics. Given their lower BRAF mutation rates and the limited efficacy of current ICI treatments, these findings emphasize the urgent need for optimize immunotherapy strategies in Japanese melanoma patients.
Keywords: Clinical subtype; Malignant melanoma; Statistics; Survival.
© 2025. The Author(s) under exclusive licence to Japan Society of Clinical Oncology.