Malignant melanomas are rarely occurring tumors, and mucosal melanoma accounts for 9% of all malignant melanomas in Japan. Primary sinonasal mucosal melanoma is an aggressive tumor with a high metastatic potential and poor outcomes. Spontaneous regression of primary cutaneous melanoma has been reported in 10%–35% of cases, but regression of a mucosal melanoma is rather rare. We report the case of an 86-year-old woman with a black tumor in the right nasal cavity. A diagnosis of malignant melanoma was made based on biopsy, but while her biopsy results were awaited, her tumor spontaneously regressed. We initially considered the use of immune checkpoint inhibitor therapy with the involvement of the oncology department of our hospital, but then decided to only follow up the patient closely. The black tumor reappeared at the same site 91 days after the first biopsy. Based on the second biopsy, the lesion was diagnosed as a malignant melanoma (T3N0M0). Endoscopic nasal tumorectomy was performed, followed by the start of immunotherapy (nivolumab) on day 26 after the surgery. Subsequently, while no local recurrence was observed, metastases were detected in the right submandibular lymph node, right lung, liver, and retroperitoneum. We switched the treatment to a two-drug regimen (ipilimumab/nivolumab), but the immunotherapy proved ineffective and the treatment was discontinued on day 404 after surgery due to progression of systemic metastases.
Spontaneous regression of malignant melanoma is thought to occur via the host immune response to the tumor. Although spontaneous regression of some primary cutaneous malignant melanomas has been reported, there is no consensus on whether the transient spontaneous regression affects the prognosis of these patients. Spontaneous regression of mucosal malignant melanomas is so rare that in our patient, we could not determine whether or when the tumor might reappear and what the patient prognosis might be. It is necessary to follow up these patients closely so that there is no delay in the treatment.
