SABR demonstrates safety and local control in primary renal cell carcinoma

Long-term follow-up results from the phase 2 TROG 15.03 FASTRACK II trial (NCT02613819) support the safety and local control of stereotactic ablative body radiotherapy (SABR) as a non-surgical treatment option for patients with inoperable or high-risk primary renal cell carcinoma (RCC).¹

The data were presented at the European Society for Radiotherapy and Oncology 2026 Congress in Stockholm, Sweden and concurrently published in The Lancet Oncology.

About the FASTRACK II study

The study enrolled 71 adult patients with primary RCC who were medically inoperable, high risk, or declined surgery. Patients needed to have an ECOG performance status of 2 or less, tumors 10 cm or less in size, and N0–N1 disease. The median age was 77 years (IQR, 70 to 82). Among all patients, 34% had T1a disease, 56% had T1b disease, 9% had T2a disease, and 1% had T3a disease.

Participants received either a single fraction SABR of 26 Gy for tumors 4 cm or less in maximum diameter, or 42 Gy in 3 fractions delivered 48 hours apart for tumors more than 4 cm in maximum diameter. The primary end point was freedom from local progression after SABR per RECIST criteria. The median follow-up was 62 months (IQR, 60 to 72).

There were no instances of local recurrence observed in the trial; local control was 100% at 36 months, 60 months, and 84 months. Partial responses were recorded in 11% of patients at 12 months, 22% at 24 months, 24% at 42 months, 33% at 60 months, and 33% at 72 months.

Cancer-specific survival was also 100% throughout the trial. The estimated distant progression-free survival was 97% (95% CI, 89 to 99) at 36 months, 88% (95% CI, 75 to 95) at 60 months, and 78% (95% CI, 50 to 92) at 84 months.

At the time of data cutoff, there were 21 overall survival (OS) events. OS was estimated to be 82% (95% CI, 70 to 89) at 36 months, 70% (95% CI, 57 to 80) at 60 months, and 64% (95% CI, 49 to 75) at 84 months.

In terms of safety, 10% of patients experienced at least 1 grade 3 adverse event (AE) that was determined to be possibly, probably, or definitely related to treatment, all occurring within 9 months of SABR. There were no grade 4 or 5 treatment-related AEs reported. No treatment-related deaths or new emergent safety signals were observed.

Limitations and conclusions

The authors acknowledged several limitations of the current study, including the small sample size, the lack of a control arm, and the potential variability in definitions of operability or technically high risk. They pointed to an ongoing study, RAPSTAR, which will randomly assign patients with T1a and T1b disease to either SABR or partial nephrectomy.

“Until the results of randomized studies are available, SABR should be delivered as an individualized treatment approach as part of a collaborative decision-making process involving patients,” the authors wrote.

Notably, the National Comprehensive Cancer Network (NCCN) 2026 guideline includes SABR as a Category 2A recommendation for some patients with T1a disease as an alternative to surgery and thermal ablation and as a preferred option for patients with T1b disease over thermal ablation. The NCCN also designed SABR a Category 2B recommendation for non-optimal surgical candidates with stage 2 disease and as a Category 3 recommendation for non-optimal surgical candidates with stage 3 disease. Similarly, the European Association of Urology 2025 guidelines recognize SABR and thermal ablation as options for medically inoperable patients with biopsy-confirmed localized disease.

“Results from the longer-term follow-up of FASTRACK II suggests that oncological and nephron-sparing outcomes after SABR are reassuringly consistent with initial reports, concordant with increasing adoption into clinical practice,” the authors concluded. “Particularly for those patients with clinically significant tumors not suitable for surgery, based on the current evidence, SABR appears to be a favorable treatment strategy.”

REFERENCE

1. Siva S, Pryor D, Martin J, et al. Long-term outcomes of stereotactic ablative body radiotherapy for primary kidney cancer (TROG 15.03 FASTRACK II): a multicentre, non-randomised, phase 2 study. Lancet Oncol. 2026;27(6):711-720. doi:10.1016/S1470-2045(26)00091-4