Case Report: Kidney preservation using immune checkpoint inhibitors in Muir-Torré syndrome-associated upper tract urothelial carcinoma, with literature review.

Mismatch repair-deficient tumors exhibit high sensitivity to immune checkpoint inhibitors. While "watch and wait" organ preservation strategies following clinical complete response are increasingly established in rectal cancer, their application to non-rectal malignancies remains experimental. This report summarizes emerging evidence regarding non-operative management, specifically recent pivotal data on tumor-agnostic responses, and contextualizes these findings through a representative case of MSH6-deficient upper tract urothelial carcinoma. Recent prospective data suggest early substantial clinical complete response rates in selected non-rectal mismatch repair-deficient tumors (approximately 65%), enabling initial non-operative management in selected patients. We present a case of high-grade upper tract urothelial carcinoma in a patient with Muir-Torré syndrome treated with definitive pembrolizumab. The patient achieved a deep clinical response characterized by complete metabolic and endoscopic resolution, with no evidence of invasive carcinoma on biopsy, resulting in successful kidney preservation without surgery. Immunotherapy-based organ preservation may represent a viable strategy for highly selected patients with mismatch repair deficiency. This approach offers a potential selective alternative to immediate radical nephroureterectomy in deep responders, provided that strict and intensive surveillance protocols are feasible.