Spontaneous Regression of Clear Cell Renal Cell Carcinoma Metastases or Immune Restoration?

Spontaneous regression of metastatic renal cell carcinoma is a rare and incompletely understood phenomenon. We report the case of a 61-year-old man with biopsy-proven pulmonary metastases from clear cell renal cell carcinoma who experienced durable tumor regression without receiving any systemic therapy. The patient underwent cryoablation of a symptomatic iliac bone metastasis and discontinued methotrexate, previously prescribed for inflammatory polyarthritis. Serial imaging demonstrated initial slow progression followed by significant shrinkage of pulmonary and mediastinal lesions, leading to a sustained partial response according to RECIST 1.1 criteria. No disease progression has been observed after extended follow-up. Two non-mutually exclusive mechanisms may explain this observation: restoration of antitumor immunity following withdrawal of immunosuppressive therapy, and a systemic immune response triggered by local tumor destruction (abscopal effect). Although such events are exceptional, this case highlights the potential interplay between immune modulation and local therapies in renal cell carcinoma. Further investigation is warranted to better understand these mechanisms and their potential therapeutic implications.