Outcomes of High-Dose Stereotactic Ablative Radiotherapy to All/Multiple Sites for Oligometastatic Renal Cell Cancer Patients

Abstract

Background: Stereotactic ablative body radiotherapy (SABR) is one of the treatment options for oligometastatic renal cell carcinoma (RCC) but is limited by a lack of data to evaluate high-dose SABR to all/multiple sites. Objective: This study retrospectively investigated the efficacy and prognostic factors of high-dose SABR for oligometastatic RCC patients. Design, setting, and participants: Patients with oligometastatic RCC on systemic therapy were retrospectively collected. Intervention(s): All patients were treated with SABR (40–50 Gy/5 fractions) for small tumors or partial-SABR (tumor center boosted with 6–8 Gy/3–5 fractions with 50–60 Gy/20–25 fractions to the whole tumor volume) for bulky tumors or tumors adjacent to critical organs. Outcome measurements and statistical analysis: Progression-free survival (PFS) and overall survival (OS) were calculated. Results and limitations: In total, 35 patients were enrolled, of which 88.5% had intermediate- or high-risk disease, with 60% on second- to fourth-line systemic therapy. The median follow-up time was 17 months. The median PFS and OS times were 11.3 and 29.7 months, respectively. Univariate analysis showed that an OS benefit was found in patients who received radiation before tyrosine kinase inhibitor (TKI) failure (p = 0.006) and where there was a short time interval (<six months) from being diagnosed with metastatic disease to undergoing radiotherapy (p = 0.046). Similar results were also found in PFS in patients who received radiation before TKI failure (p = 0.049) or within eight months (p = 0.047). There were certain differences in PFS (p = 0.033) between patients receiving radiotherapy with all lesions and those with selected tumors. In multivariate analysis, OS benefits were found in patients who received radiotherapy before TKI failure (p = 0.028). The limitations of this study include its retrospective design and the small patient cohort. Conclusions: The early use of high-dose SABR to multi-lesions may improve survival. Partial-SABR for bulky lesions close to critical organs could be safely and effectively applied under certain circumstances.