Primary melanoma of the urinary tract; Clinicopathologic and molecular review of a case series.

Primary melanoma of the urinary tract is a very rare and aggressive cancer. It accounts for less than 1% of all the melanoma cases, making it difficult to histopathologically diagnose and manage. We present a retrospective case series of eight primary urinary tract melanoma with clinical, pathological, and molecular findings to add more insight to this challenging disease. These cases were evaluated for histopathological, immunohistochemical, and molecular features of melanoma that were most commonly found in the urethra, followed by those in the bladder and ureter. Identification of nested growth patterns and in situ melanocytic components at cell edges are helpful in the histopathological diagnosis of amelanotic or hypomelanotic tumors. Our results indicate that urinary tract melanoma has several molecular traits, such as gene expression patterns. Genetic mutations may be related to metastasis, as well as provide targets for the management programs.