Malignancies in horseshoe kidneys: an updated review

Out of over 4000 available studies about horseshoe kidney (HSK), we selected 89 representative articles that emphasized the most common genetic lesions and tumors that can occur in these patients. Renal cell carcinomas, carcinomas of the urothelial tract, and Wilms tumor are the most common primary tumors reported to be associated with HSK. Besides a literature review, we present the 39th case of a neuroendocrine neoplasm (NEN) in an HSK, reported to date in Medline/Web of Science-indexed literature. From the 127 NENs of the kidneys reported till 2025, including our case, 39 associated HSK (30.71%). Based on an extensive literature review, a hypothesis regarding tumorigenesis inside of HSK is also formulated.