Invasive High-grade Upper Tract Urothelial Carcinoma in a 14-Year-Old Girl.

We present an unusual pediatric case of invasive upper tract urothelial carcinoma with an associated genetic predisposition. A 14-year-old female presented with intermittent right flank pain, and was found to have a poorly functioning hydronephrotic right kidney. Laparoscopic nephrectomy was performed. Pathology demonstrated upper tract urothelial carcinoma, and she subsequently underwent completion ureterectomy. Genetic studies demonstrated a double-hit constitutional deletion of a DNA mismatch repair protein, revealing a rare Lynch syndrome variant known as Constitutional Mismatch Repair Deficiency Syndrome. This disease places her at high risk for multiple malignancies, including upper tract urothelial carcinoma.