FASTRACK II NCT02613819
ForPrimary RCC ≤10cm, T1b-dominant, medically inoperable or declined surgery
100% at 36, 60, 84 mo
ITT population, RECIST-assessed, median f/u 62 mo
TL;DR100% freedom from local progression at 36, 60, and 84mo after single-fraction 26Gy or 42Gy/3fx SABR in inoperable primary RCC.
The transferable detail is the size-adapted prescription: 26Gy in one fraction under 4cm, 42Gy/3fx above it, with median tumour 46mm and 65% T1b or higher. That is a larger-tumour cohort than most ablation series, and zero local failures out to 84mo supports offering SABR when a 77-year-old is turned down for nephrectomy.
In a medically inoperable or surgery-declining patient with a primary RCC up to 10cm, including T1b and larger where thermal ablation is a poor fit, this supports SABR as a durable local option; it does not speak to the operable patient, where nephrectomy remains untested against it.
The transferable detail is the size-adapted prescription: 26Gy single fraction under 4cm, 42Gy/3fx above it, in a cohort with median tumour 46mm and 65% at least T1b. Zero local failures to 84mo supports offering SABR when the patient is turned down for nephrectomy; bowel toxicity (two colonic obstructions) sets the technical ceiling.
This is the non-surgical arm of the small-renal-mass conversation getting real prospective follow-up, at a median tumour of 46mm where thermal ablation performs worst. It changes what you can tell a high-risk or surgery-declining patient at referral; it does not test SABR against partial nephrectomy in an operable patient, which remains unstudied.
10 details
Non-randomised phase 2, eight hospitals in Australia and the Netherlands, run by TROG and ANZUP. Enrolment July 28 2016 to Feb 27 2020; 71 enrolled, one withdrew consent before treatment. This report is the pre-planned final follow-up at a median of 62 months (IQR 60-72).
Histologically confirmed primary RCC, medically inoperable, high risk, or declined surgery, ECOG ≤2, tumours ≤10 cm, N0-N1. Median age 77 years (70-82), 49 (70%) male. Median tumour size 46 mm (37-55), with 39 (56%) T1b, six (9%) T2a and one (1%) T3a.
Size-adapted prescription: 26 Gy in a single fraction for tumours ≤4 cm, 42 Gy in three fractions 48 h apart for tumours >4 cm. Histological confirmation was required before treatment, so this is a biopsy-proven cohort rather than a radiographic-diagnosis one.
Primary: freedom from local progression by RECIST, assessed in the intention-to-treat population, as was safety.
100% local control at 36, 60 and 84 months, with no local recurrences and no cancer-related deaths reported in the cohort.
Seven (10%) patients had at least one treatment-related grade 3 event within 9 months: pain in four (6%), nausea and vomiting in three (4%), colonic obstruction in two (3%), diarrhoea in one (1%). No grade 4 events and no treatment-related deaths; no new long-term safety signals emerged with extended follow-up.
A 100% point estimate in 70 pts carries a wide confidence bound that the headline hides, and RECIST is an imperfect local-control instrument after ablative RT, where a treated mass commonly persists without viable tumour. Renal function trajectory, the endpoint that actually competes with nephrectomy, is not reported in this source.
Prior SABR evidence in primary RCC was retrospective and pooled, so a prospective multicentre dataset at 84 months is the new contribution rather than the effect size itself. Comparison to partial nephrectomy and thermal ablation remains indirect: no randomised trial has run, and this cohort was selected against surgery by definition.
The finding that transfers is durability at a tumour size where thermal ablation performs worst, with a median of 46 mm and 65% at least T1b. What it does not settle is whether SABR is a choice rather than a fallback, which needs a randomised or matched comparison in operable pts, with renal function as a co-primary.
Single-arm phase 2, N=70, inoperable or surgery-declining pts only. No randomised comparator vs partial nephrectomy or thermal ablation. Maturity gate holds despite 62mo f/u.
- SABR vs partial nephrectomy in operable pts
- Renal function trajectory after SABR vs nephrectomy
- SABR vs thermal ablation in T1b tumours
📚 Sources · 📄 1 paper
Abstract
The longer read
The number that will get quoted from this readout is 100% freedom from local progression, sustained at 36, 60, and 84 months, and it is worth being precise about what that number can and cannot support. It is a point estimate in 70 treated patients from a single-arm cohort, so its lower confidence bound is meaningfully below 100% even though the abstract prints no interval. What is genuinely new is not the magnitude, which prior retrospective and pooled SABR series had already pointed toward, but the design and the duration: a prospective multicentre trial across eight hospitals in two countries, with a pre-planned final analysis at a median 62 months of follow-up and local-control estimates carried out to 84 months. Renal SABR has been short on that kind of evidence, and the absence of late local failures answers the specific worry that ablative doses to a slow-growing tumour merely defer recurrence past the usual reporting window.
The cohort composition matters more than the headline for anyone deciding whether this transfers. Median tumour size was 46 mm, with 39 (56%) T1b, six (9%) T2a, and one (1%) T3a, so roughly two thirds were at least T1b. That is the size range where percutaneous thermal ablation is least reliable, and it is the reason this dataset is not simply a slower alternative to cryoablation or radiofrequency in the small renal mass. The size-adapted prescription is the other half of the transferability question: 26 Gy in a single fraction under 4 cm, 42 Gy in three fractions 48 h apart above it. Both are deliverable in a standard SABR program, which is not true of every ablative renal protocol reported to date.
Against that, the population was defined by being unsuitable for or unwilling to have surgery, median age 77, ECOG up to 2. Selection cuts both ways here. It plausibly enriches for competing mortality, which shortens the window in which a local failure could ever be observed, and it also means the comparison a urologist actually wants, SABR versus partial nephrectomy in an operable patient, is untouched. No randomised trial has attempted that question, and this trial was not designed to. Reading the result as evidence that SABR matches surgery goes well past what the design permits.
Two methodological points should move confidence in opposite directions. RECIST is a blunt instrument for local control after ablative radiotherapy, where a treated mass frequently persists on imaging without viable tumour; that biases toward calling failures, not away from them, so a 100% result under RECIST is a harder result than it would be under a size-plus-enhancement definition. Working the other way, biopsy confirmation was required, which removes the benign-lesion contamination that inflates control rates in radiographically diagnosed ablation series. The grade 3 toxicity rate of 10% within nine months, including two colonic obstructions, is the honest counterweight: these are large upper-abdominal targets and bowel is the organ at risk that will define the technical ceiling.
What would have to be true for this to mislead? Chiefly, that the observed durability reflects a cohort whose competing mortality outran their tumours. Median follow-up of 62 months in a 77-year-old population argues partly against that, but the trial reports no renal function trajectory in this source, and renal preservation is the endpoint on which SABR would win or lose an argument against nephrectomy.