Stereotactic ablative radiation therapy for oligometastatic renal cell carcinoma (SABR ORCA): a meta-analysis of 28 studies

The use of stereotactic ablative radiotherapy for recurrent and metastatic renal cell carcinoma (RCC) is not yet standard treatment due to uncertainties regarding its efficacy and safety. The objective of the systematic review and meta-analysis was to assess the efficacy and safety of stereotactic radiotherapy for metastatic RCC. A Population, Intervention, Control, Outcome, Study Design (PICOS)/Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)/Meta-analysis of Observational Studies in Epidemiology (MOOSE) protocol was utilized to select studies published during 1998–2019. The primary outcome was 1 year local control and 1 year overall survival; the secondary outcome was Common Terminology Criteria for Adverse Events grade 3–4 toxicity. Weighted random-effect meta-analyses were conducted using the DerSimonian and Laird method, heterogeneity was evaluated using the I2 statistic and Cochran Q test, and the Egger test assessed publication bias. A total of 265 studies were screened and 28 studies were included. There were 1602 mutually exclusive patients (679 extracranial/923 intracranial) and 3892 lesions (1159 extracranial/2733 intracranial). The median age was 62 yr. The median treatment volume was 59.7 cc for extracranial (interquartile range: 31.1–71.4) and 2.3 cc for intracranial (interquartile range: 1.3–4.3) lesions. Under the random-effect model, the summary effect size for 1-yr local control was 89.1% (95% confidence interval [CI]: 83.6–93.7%, I2 = 71%) and 90.1% (95% CI: 83.5–95.3%, I2 = 74%) for extracranial and intracranial disease, respectively. The 1-yr survival rates were 86.8% (95% CI: 62–99.8%, I2 = 95%) and 49.7% (95% CI: 41.1–58.3%, I2 = 74%) for extracranial and intracranial disease, respectively. The incidence of any grade 3–4 toxicity was 0.7% (95% CI: 0–2.1%, I2 = 0%) for extracranial disease and 1.1% (95% CI: 0–7.4%, I2 = 53%) for intracranial disease. Stereotactic radiotherapy is safe and efficacious for RCC oligometastases, with local control at 90% and any significant toxicity at 1%, reported at 1 yr. Further prospective studies are needed. Stereotactic radiotherapy is safe and effective in treating kidney cancer that has spread to other parts of the body: 90% of cancers do not progress in the treated region and <1% of patients have side effects at 1 yr.