STEREOTACTIC ablative body radiotherapy demonstrates durable long term local control in patients with primary renal cell carcinoma, according to final results from the FASTRACK II phase 2 trial conducted across Australia and the Netherlands.
Trial Design and Patient Population
The FASTRACK II study was a non-randomised phase 2 trial led by the TransTasman Radiation Oncology Group and the Australian and New Zealand Urogenital and Prostate Cancer Trials Group. The study evaluated stereotactic ablative body radiotherapy as a non-invasive alternative for patients with primary renal cell carcinoma who were medically inoperable, at high surgical risk, or who declined surgery.
A total of 71 adult patients were enrolled across eight hospitals, with one patient withdrawing before treatment. The median follow-up period was 62 months, and the median age was 77 years. Most participants had early-stage disease, with the majority classified as T1b or higher, and the cohort included patients with tumours up to 10 cm in size.
Patients received either a single 26 Gy fraction for tumours measuring 4 cm or less, or 42 Gy delivered in three fractions for tumours larger than 4 cm.
Long Term Efficacy Outcomes
The primary endpoint of the study was freedom from local progression, assessed using Response Evaluation Criteria in Solid Tumours criteria. Across follow-up periods extending to 84 months, stereotactic ablative body radiotherapy achieved 100% local control, with no reported local recurrences in the treated cohort.
Investigators reported no cancer related deaths during follow-up, supporting sustained disease control in a population largely unable to undergo surgical intervention.
Safety And Clinical Implications
Safety analysis showed that 10% of patients experienced grade 3 adverse events within nine months of treatment that were considered possibly, probably, or definitely related to stereotactic ablative body radiotherapy. Reported events included nausea and vomiting, abdominal or tumour related pain, colonic obstruction, and diarrhoea.
Importantly, no new long term safety signals, grade 4 toxicities, or treatment related deaths were observed during extended follow-up.
These findings suggest that stereotactic ablative body radiotherapy may offer a durable, non-invasive treatment option for selected patients with renal cell carcinoma who are unsuitable for surgery, with sustained local control and an acceptable safety profile over long term follow-up.
Reference
Siva S 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. The Lancet Oncology. 2026;27:711-20.
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