Urological Melanoma: A Comprehensive Review of a Rare Subclass of Mucosal Melanoma with Emphasis on Differential Diagnosis and Therapeutic Approaches

SIMPLE SUMMARY: Mucosal melanoma accounts for only about 1% of all melanoma cases worldwide, but achieving the correct recognition, diagnosis and prognosis is of extreme importance for the patient. Moreover, primary melanoma of the urinary tract is a rarity among rarities, accounting for less than 4% of all the mucosal melanomas. The urethra is the most common location for this type of melanoma, followed by the bladder and ureter with decreasing incidences. Patients with this form of melanoma are usually elderly (over 60 years) and asymptomatic or have hematuria symptoms. Compared to other mucosal melanomas, there is not much knowledge of the risk factors, etiology, and molecular characteristics of urological melanoma. In addition, there are no uniform staging systems or treatment protocols available for this disease. A thorough knowledge of the existence and management of this disease entity is essential to allow research advances in this area and, in particular, to devise innovative therapies. In this paper, we focus in detail on melanoma originating from the uropoietic apparatus, discuss the cases reported in literature of this very rare and still partially enigmatic melanoma subclass, and consider the scenario leading to metastasization to neighboring organs. ABSTRACT: Melanoma is reported as the 19th most common cancer worldwide, with estimated age-standardized incidence rates of 2.8–3.1 per 100,000. Although the origin is most frequently cutaneous, mucosal melanoma has been described several times in literature, and despite its rarity (only 1% of all melanomas), increasing attention is being paid to this disease form. Within this subgroup, melanomas of the uropoetic apparatus are a rarity among rarities. Indeed, less than 50 cases of primary melanoma originating from the urinary bladder have been described, and even less originating from the kidney, renal pelvis and urethra. In this work, we present a detailed review of the literature related to this subclass of mucosal melanoma, delve into the biological landscape of this neoplasm and discuss current approaches, future perspectives and potential therapeutic approaches.