Case Report: Spontaneous regression of cystic renal cell carcinoma

Spontaneous regression (SR) of cystic renal cell carcinoma (CRCC) is extremely rare, and previous reports lack pathological confirmation. In this review, we report a case of spontaneous partial regression of Bosniak grade IV CRCC confirmed by postoperative pathology, and discuss its potential mechanism.

A 59-year-old female patient with a simple cyst (34*31 mm) in her left kidney was detected by color doppler flow imaging(CDFI) in July 2023. In October 2024, the computed tomography(CT) showed that the lesion had progressed to Bosniak grade IV cystic mass (60*50 mm), which was not treated. Follow-up magnetic resonance imaging (MRI) in April 2025 showed that the lesion was significantly reduced (25*28 mm). The patient underwent robot-assisted laparoscopic partial nephrectomy, and was pathologically diagnosed with clear cell renal cell carcinoma(ccRCC) after surgery.

Despite spontaneous regression, Bosniak grade IV renal cystic disease requires surgical intervention to confirm the diagnosis and avoid progression. This study provides a new basis for the natural history of high-risk renal cystic lesions and individualized follow-up strategies.