Horseshoe kidney with renal parenchymal squamous cell carcinoma: a case report and comprehensive literature review.

Horseshoe kidney (HSK) complicated with renal parenchymal squamous cell carcinoma (RSCC) is exceedingly rare and clinically insidious. Owing to the absence of pathognomonic symptoms or imaging hallmarks, the malignancy is frequently obscured by coexistent renal calculi, hydronephrosis, or infection, resulting in formidable diagnostic challenges, missed diagnoses, and consequently delayed treatment. We report a 60-year-old man who presented with HSK, left renal calculi, and hydronephrosis. After comprehensive preoperative evaluation, laparoscopic radical nephrectomy with isthmic transection was performed; histopathology confirmed a moderately to well-differentiated RSCC. A systematic literature review contextualizes this exceptional association. Clinicians should maintain a high index of suspicion for RSCC in HSK patients with long-standing calculi or anatomical anomalies who present with refractory flank pain. Early radical nephrectomy with regional lymphadenectomy remains the treatment of choice. Immunotherapy holds promise, yet its efficacy requires validation in prospective studies.