Retrospective analysis of patients undergoing stereotactic body radiotherapy (SBRT) in secondary non-bone lesions of metastatic renal cell carcinoma (mRCC) in treatment with vascular endothelial growth factor (VEGF) tyrosine kinase inhibitors

Aims: A traditionally radioresist tumor such as mRCC nowadays showed in several studies good response rates to radiotherapy treatment of metastatic lesions. While most of these studies include patients with secondary bone lesions, today there is no prospective or retrospective study on the use of radiotherapy in patients with non-bone mRCC metastases in order to consolidate the response to medical therapy (TKI or mTOR inhibitors) or to treat the individual oligoprogression sites. Primary outcome of the study was to evaluate the response rate of non-bone lesions treated with SBRT according to RECIST 1.1 criteria in patients with renal carcinoma who were previously subjected to oncological treatment with medical therapy (Sunitinib or Sorafenib), at Azienda Ospedaliero-Universitaria in Parma. Methods: From April 2016 to February 2017 retrospective data were collected from 9 patients treated at Azienda Ospedaliero-Universitaria in Parma, all living, 2 females and 7 males, avarage 65.3 years of age (57- 80 years) with SBRT-treated non- skeletal metastases on one site. Range doses were 15 Gy – 45 Gy (average 33 Gy) in 1 to 5 fractions (average 4 fractions). All patients were treated with antiangiogenetic medications. The SBRT treated metastases were located at brainstem (1 case), lung (2 cases), chest thoracic lymph node (1 paratracheal, 1 peripheral and 1 parasternal), paraortic lymph node (1 case), ileo-psoas region (1 case), supraclavicular region (1 case). All patients were followed up with CT every 3-4 months. The answer was evaluated using the Recist 1.1 criteria. Results: After SBRT treatment, 77,8% of patients showed metastasis volumetric reduction, while 22,2% of patients reported dimensional stability of the lesion, without toxicity due to the treatment, and also having a periodical suspension of terapy with mTOR inhibitors or TKI. Conclusions: This study showed that the combination of SBRT on metastatic lesions of renal cell carcinoma and TKI or mTOR inhibitors allows good local and systemic control of desease in a significant percentage of patients. Because of the limited number of patients in the analyzed sample the statistical study is not significant, but this trend is very interesting and important for new set of treatment of this patients. For this reason we are planning a multicentre retrospective study to confirm this trend, obtain more informations on this kind of approach and start to evaluate other new indications for SBRT.