Discussion:

Cutaneous melanoma is considered the most lethal primary neoplasm of the skin (1). It has an incidence of 17 and a mortality rate of 2.2 per 100 000 persons in the United States (2). Approximately 30% of the patients with melanoma will develop a metastatic disease, especially in organs like the lungs, skin, brain and liver. Metastases to the bladder are extremely rare, and until 2022, only 29 cases have been reported in the English literature (3). However, this number can be underestimated and numerous cases of metastatic melanoma to the bladder can remain undiagnosed, because an autopsy series of patients with metastatic melanoma found a rate between 18%-37% of metastatic disease to the bladder.

Once the melanoma has developed a metastatic disease, the prognosis is considered generally poor. The 5-year survival rate in patients with stage IV metastatic disease is 29.8% in the United States (1). The location of the initial metastatic site, apparently, is a significant predictor of survival, with a lower survival associated rate with distant nodal involvement, gastrointestinal, lung, bone, liver, and brain metastasis. It is not clear if bladder metastases are correlated with a worse outcome, due to the few cases reported of this clinical presentation.

Like our case report, patients with metastatic melanoma to the bladder can be asymptomatic or can develop a symptomatology that includes hematuria, urinary retention, voiding symptoms, dysuria, urinary frequency, suprapubic pain, flank pain and weight loss (4). The immunohistochemistry is an essential tool for the confirmation of metastatic melanoma, demonstrating expression of f S-100, HMB-45, MART-1/Melan-A, tyrosinase, and MITF (4). The microscopic features can include spindled or epithelioid cells (with marked pleomorphism, abundant cytoplasm, and a prominent eosinophilic nucleoli), necrosis, mitotic figures and atypical melanocytes.