Two small studies looked at the addition of a type of radiotherapy treatment, called stereotactic body radiotherapy (SBRT), to treatment with a tyrosine kinase inhibitor (TKI), such as sunitinib or pazopanib, or a checkpoint inhibitor, such as nivolumab for patients with metastatic renal cell carcinoma (RCC).

In the first study, 56 patients with metastatic RCC were treated with a TKI and SBRT for tumours that could not be removed with surgery. The patients were followed-up for a median of 21.7 months. Median overall survival was 61.2 months, median progression-free survival was 11.5 months and the 2-year local control rate was 94%.

In conclusion, SBRT plus TKI treatment is safe and seems to improve survival in patients with metastatic RCC. Patients who received SBRT before TKI treatment stopped working have a higher complete response rate, and the favourable local response might improve survival.

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In the second study, 17 patients with stable disease for at least 4 months on TKI or checkpoint inhibitors were treated with SBRT directed at an organ with at least two comparable metastases. One of the metastases was intentionally left untreated (control lesion) while the other was treated with SBRT. Response was measured in both metastases 2 months after SBRT. In 13 patients (76%), the SBRT-treated metastasis responded to treatment, and 5 patients (29%) had a complete response. Eight patients (47%) had a partial response. The control lesions remained stable in 16 patients. There was a statistically significant difference between the mean sizes of the target and control lesions before and at 2 months after SBRT.

In conclusion, SBRT in metastatic RCC patients treated with TKI or checkpoint inhibitors is well tolerated and could be effective.

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