This phase 2 study looked at the use of stereotactic radiotherapy to treat metastatic renal cell carcinoma (RCC) in patients where the cancer had spread and there were a small number of metastases. These patients were on a tyrosine kinase inhibitor as the first or second medicine for their cancer. The aim of the study was to see if stereotactic radiotherapy could control the cancer at 1 year.
Patients had clear cell RCC, were generally healthy and had favourable or intermediate risk disease. They were also on TKI treatment for at least 3 months and had 5 or less metastases. If metastases were stable or responding to TKI treatment they were not treated with stereotactic radiotherapy.
The study was closed early because of slow patient recruitment, with 38 patients. 37 patients had 57 metastases treated with stereotactic radiotherapy. Stereotactic radiotherapy failed in only 2 patients, resulting in a control rate of 93% at 1 year. In addition, metastases grew in 21 patients outside the areas treated with stereotactic radiotherapy. The average time to when the cancer started growing again and the treatment stopped working (progression-free survival) was 9.3 months. Most side effects to stereotactic radiotherapy were mild, and there were no life-threatening side effects or deaths during the study.
Despite closing early, this is one of the largest studies of stereotactic radiotherapy for metastatic RCC and shows promise for this type of treatment at controlling the cancer and delaying the need to change medicines. The role of stereotactic radiotherapy needs further investigation with immunotherapy combinations.