Clinical Features and Management of Primary Neuroendocrine Tumors in Rare Sites of the Urinary System: Two Case Reports and Literature Review

Background: Neuroendocrine tumors (NETs) primarily arising within the urinary system, particularly in the kidney or testis, are extremely rare. This rarity often results in diagnostic delays and therapeutic uncertainty. Heightened clinical vigilance is warranted for urogenital masses exhibiting atypical features and negative conventional tumor markers. Case presentation: We report two rare cases of primary urinary NETs. The first case involved a 52-year-old woman with an incidentally discovered left renal mass, ultimately diagnosed as a well-differentiated renal NET based on characteristic histological features and immunohistochemical (IHC) positivity for synaptophysin (Syn) and INSM1. The second case was a 21-year-old man who presented with painless right testicular enlargement, and was diagnosed with primary prepubertal-type testicular NET. Metastatic disease was excluded in both cases through comprehensive imaging and IHC analyses. Both patients underwent complete surgical excision and remained disease-free during follow-up. Conclusion: Primary renal and testicular NETs should be considered in differential diagnoses of atypical urogenital masses. Definitive diagnosis requires integrated histopathological assessment with targeted IHC and metastasis exclusion. Complete surgical resection remains the cornerstone of management, with mandatory long-term surveillance due to metastatic potential.