Toripalimab in Metastatic Renal Collecting Duct Carcinoma: A Case Report

Introduction: Collecting duct carcinoma (CDC), a rare and highly aggressive subtype of renal cell carcinoma (RCC), is often associated with poor prognosis due to its resistance to conventional therapies. Although platinum-based chemotherapy is conventionally regarded as the first-line treatment of metastatic CDC, its clinical benefits are limited. Emerging evidence suggests that CDC shares immunophenotypic and genomic features with urothelial carcinoma, providing a rationale for investigating immune checkpoint inhibitors. Case Presentation: We report the case of a 55-year-old male patient with postoperative metastatic CDC exhibiting a urothelial carcinoma-like immunophenotype. The patient presented with gross hematuria and left flank pain, and imaging revealed a large left renal mass with regional lymph node and pulmonary metastases. Histopathology confirmed CDC, characterized by high nuclear atypia, extensive necrosis, and high Ki-67 proliferation. First-line gemcitabine-cisplatin chemotherapy was discontinued due to grade III gastrointestinal toxicity, leading to imitation of second-line treatment with toripalimab, a programmed death protein 1 (PD-1) inhibitor. The patient achieved a complete response after six cycles of toripalimab, confirmed by the complete resolution of bilateral pulmonary metastases. Immune-related adverse events were managed with temporary treatment interruption, prednisone, and L-thyroxine therapy. Currently, the patient has maintained a progression-free survival of 24 months. Conclusion: This case demonstrates the complete response of metastatic CDC to toripalimab, despite negative PD-L1 expression. This outcome highlights the role of CD8+ T-cell infiltration and IFN-γ pathway activation within the tumor microenvironment in treatment response and the potential efficacy of PD-1 inhibition as a viable therapeutic strategy for this aggressive RCC subtype.