Survival Outcomes After Adding Stereotactic Body Radiotherapy to Metastatic Renal Cell Carcinoma Patients Treated With Tyrosine Kinase Inhibitors

Objective: Long-lasting control is rarely achieved with tyrosine kinase inhibitors (TKI) alone in metastatic renal cell carcinoma (mRCC). Our study aimed to investigate the survival outcomes of adding stereotactic body radiotherapy (SBRT) to TKI in mRCC. Materials and Methods: From September 2015 to September 2018, 56 patients treated with TKI received SBRT for 103 unresectable lesions. A total of 24 and 32 patients were irradiated before and after TKI failure, respectively. Overall survival (OS) was calculated from metastases. Progression-free survival (PFS) was calculated from SBRT. Results: Overall, 10, 32, and 12 patients had International Metastatic Renal Cell Carcinoma Database Consortium favorable, intermediate, and poor risk. Median follow-up was 21.7 months (range, 5.1 to 110.6 mo). Median OS was 61.2 months. The median PFS was 11.5 months, while the 2-year LC rate was 94%. Sixteen (34%) lesions achieved complete response (CR) in patients irradiated before TKI failure, whereas only 4 (7%) lesions yielded CR in those irradiated after TKI failure (P=0.001). The median PFS in CR group was significantly longer than that of non-CR group (18.9 vs. 7.1 mo; P=0.003). The 5-year OS in CR group was 86%, compared with 48% in non-CR group (P=0.010). Four (7%) patients experienced Grade 3 toxicity. Conclusions: Adding SBRT to TKI is safe and seems to improve survival in mRCC. Patients irradiated before TKI failure have higher CR rate, and the favorable local response might turn into survival benefit.