An 83-year-old woman was referred to our hospital because of a black ulcer of the lower right gingiva. A diagnosis of malignant melanoma （T4aN1M0） was made based on biopsy by a previous doctor and imaging findings, and surgery was scheduled. However, the tumor in the oral mucosa shrank before the surgery. The patient underwent sectional mandibulectomy and right neck dissection on day 26 after initial consultation. Local control was good, but metastasis was found in the contralateral cervical lymph nodes and lungs 8 months after surgery. Chemotherapy was performed in another hospital, but the effect was insufficient and the treatment ended. After that, palliative care was mainly performed, and she died 3 years and 2 months after surgery due to cerebral hemorrhage associated with brain metastasis. Based on the clinical course and histopathological findings of surgical specimens, it was considered that oral primary malignant melanoma had undergone spontaneous partial regression.
