Melanuria is the dark brown discoloration of the urine and an uncommon manifestation in patients with melanoma. It is an ominous sign, usually indicating widespread disease. In this article, through an illustrative case, we discuss the pathophysiological, clinical, and prognostic characteristics of melanuria in melanoma. Moreover, we aim to provide the available data for the prompt diagnosis and treatment of patients presenting with melanuria. We present the case of a 47-year-old man presenting with melanuria and diffure melanosis cutis, who was eventually diagnosed with a BRAF-mutated metastatic melanoma of unknown primary. The patient was started on a BRAF and MEK inhibitor, but he had a rapid disease progression and succumbed to the disease. There is only a limited number of case reports of melanoma patients with melanuria receiving targeted therapies or immune checkpoint inhibitors. In these reports, variable treatment responses have been described. In view of the increasing significance of targeted therapies and immunotherapy for melanoma, more cases are needed to improve our understanding on the prognostic significance of melanuria in the era of novel therapies for melanoma.
The incidence of melanoma is increasing worldwide, especially in countries with moderate climates and a high percentage of sunny days during the year, alongside an increase of melanoma-related mortality.
Unlike most solid tumors, melanoma affects mostly young and middle-aged people, with a linearly increasing incidence between the ages of 25 and 50 years. Melanuria refers to the dark brown discoloration of the urine due to increased urine excretion of melanin precursors. Melanuria is not commonly observed in patients with metastatic melanoma, although it is consistently reported to occur in up to 15% of the cases, especially in patients with metastatic visceral disease. This rate might be higher than expected in clinical practice and may include cases in which brown discoloration of urine is not macroscopically apparent, but increased levels of melanin precursors can be detected with laboratory methods. Interestingly, in cases of advanced melanoma, melanuria is often associated with a diffuse skin hyperpigmentation, termed as diffuse melanosis cutis (DMC). In this article, we describe the case of a middle-aged melanoma patient presenting with melanuria and DMC who was treated with BRAF- and MEK-inhibitors.