Basaloid squamous cell carcinoma arising in [corrected] the renal pelvis.

Basaloid squamous cell carcinoma is an uncommon and highly aggressive variant that can occur anywhere squamous cancers occur. It is most often seen in the head and neck, the perianal region, and the female genital tract. It is extremely rare in the urinary system. In this article, we report the first known case of basaloid squamous cell carcinoma arising in the renal pelvis. Given the aggressive nature of this neoplasm, it should not be omitted from the differential diagnosis of neoplasms arising from the urothelium.