Belzutifan for Metastatic TFE3 ‐Rearranged Renal Cell Carcinoma With Pulmonary Metastases: A Case Report

Introduction Belzutifan is effective in patients with previously treated advanced clear cell renal cell carcinoma. However, evidence for its use in non‐clear cell renal cell carcinoma remains limited. Case Presentation A 33‐year‐old Japanese woman underwent total nephrectomy for a 10‐cm renal tumor with lung metastases. The histological and immunohistochemical results were consistent with TFE3 ‐rearranged renal cell carcinoma. She was administered belzutifan as fourth‐line therapy. Her inflammatory markers normalized. After 4 weeks, computed tomography showed a decrease in the number and size of the pulmonary metastases, although the nodal lesions and local recurrence remained stable. At 12 weeks, chest radiography revealed improvement in both the bilateral nodular lesions and infiltrative opacities. No grade ≥ 3 adverse events occurred, as supportive care for anemia‐related complications was provided. Conclusion Belzutifan led to radiographic improvement in pulmonary metastases and symptoms, while other lesions remained stable. This suggests its potential therapeutic use in TFE3 ‐rearranged renal cell carcinoma.