SABR Without Surgery Is Becoming a Real Option for Kidney Cancer
In this article
The FASTRACK II Study: Treating Kidney Cancer Without Surgery
Why has the view of radiotherapy for kidney cancer changed?
For many years, renal cell cancer was considered a tumor that was “resistant to radiotherapy.” This idea dated from the era of conventional low-dose radiotherapy delivered to large fields. However, modern radiotherapy technologies have changed this perception. SABR can deliver a very high biologically effective dose to the tumor with millimeter precision while aiming to better protect surrounding healthy kidney tissue and organs such as the bowel, stomach, liver, and spinal cord.
What we are discussing today is therefore modern stereotactic radiotherapy guided by imaging, with motion management, high doses, a very short treatment duration, and an ablative effect. FASTRACK II provides some of the strongest prospective evidence that this technology can be used as definitive treatment without surgery for primary kidney cancer.
SBRTis modern stereotactic body radiotherapy that delivers high-dose radiation to a tumor with millimeter precision, usually in a small number of sessions. SABR is the name that particularly emphasizes the “ablative” effect of SBRT's high biological dose, meaning its aim to destroy the tumor in place; the term SABR may therefore be more appropriate in settings where definitive treatment is intended, such as primary kidney cancer.
What kind of study was FASTRACK II?
FASTRACK II is an international, multicenter, non-randomized phase 2 study investigating the efficacy and safety of SABR in patients with primary renal cell cancer who did not undergo surgery. The study was conducted at seven centers in Australia and one center in the Netherlands.
The study enrolled adults with biopsy-confirmed primary kidney cancer and a single lesion who were medically unfit for surgery, had a high risk of surgical complications, or declined surgery. Patients were required to have an ECOG performance status of 0–2, and a multidisciplinary board had to consider active treatment necessary.
| Item | FASTRACK II design | Clinical meaning |
|---|---|---|
| Study type | International, multicenter, non-randomized phase 2 study | No direct comparison with surgery; strong prospective single-arm evidence. |
| Number of patients | 70 patients | One of the most important prospective cohorts for non-surgical definitive treatment in primary RCC. |
| Centers | 7 Australian centers + 1 Dutch center | Multicenter feasibility data rather than experience from a single center. |
| Eligible patient profile | Patients with primary RCC who are medically inoperable, have a high surgical risk, or decline surgery | The main evidence for SABR comes from this selected patient group. |
| Tumor size | Primary kidney tumors up to 10 cm | Important evidence that is not limited to small renal masses. |
| Important exclusion criteria | eGFR <30 mL/dk/1,73 m², direct contact between the tumor and bowel, previous overlapping high-dose RT, previous systemic RCC treatment, tumor larger than 10 cm | The results apply to patients selected for kidney function and anatomical suitability. |
How was treatment delivered?
In FASTRACK II, the SABR dose was determined by tumor size. Tumors with a maximum diameter of 4 cm or smaller received 26 Gy in a single session . For tumors larger than 4 cm and up to 10 cm, 42 Gy in 3 fractions was delivered. This is very different from the conventional radiotherapy approach of treatment over several weeks; the aim is to deliver a high biological dose over a very short period.
It means delivering radiotherapy at high doses in very few sessions. In FASTRACK II, treatment was completed in one or three sessions. This may offer a practical advantage for patients who are older, have a high surgical risk, or cannot attend hospital frequently.
The main FASTRACK II result: very high local control
The main FASTRACK II publication in Lancet Oncology in 2024 showed very strong local control after SABR for primary kidney cancer. In the study, 12-month local control was %100 . In the final long-term results, median follow-up reached 62 months and again no local recurrence was detected. No deaths due to kidney cancer were reported either.
This result is particularly important because a substantial proportion of the patients in the study were older and at risk from surgery, and their tumor characteristics represented a more complex population than simple small renal masses. According to the TROG statement, at least %70 of patients had signs suggesting more aggressive behavior, such as growth during active surveillance.
Pooled analysis: what did FASTRACK + FASTRACK II show together?
The long-term pooled analysis published in 2026 combined the FASTRACK phase 1 and FASTRACK II phase 2 studies. A total of 103 patients were evaluated. The median age was 76,9 ; this shows that the study reflects well the older patient group who are unfit for surgery in real-world practice.
Median follow-up was 5,0 years . Local control was reported as %100 at 1 year, %98 at 3 years and %98 at 5 years . Only one patient developed local progression; this occurred at month 28 together with distant progression.
Distant metastasis and long-term disease control
Although local control is close to perfect, true clinical success in kidney cancer involves more than control of the tumor bed alone. The development of distant metastasis reflects the systemic biology of the disease. News sources reported freedom from distant tumors in the pooled analysis as, at 3 years, %97, at 5 years, %88 and at 7 years, %78 .
Safety and kidney function
The safety profile in FASTRACK II was generally considered acceptable. In the main 2024 publication, grade 3 treatment-related adverse effects were reported at a rate of %10 ; no grade 4 adverse event was observed. Reported grade 3 events included nausea and vomiting, abdominal/flank/tumor pain, colonic obstruction, and diarrhea.
The safety profile was also encouraging in the 2026 pooled analysis. Grade 3 adverse events occurred in 8 patients. No grade 4 adverse event or treatment-related death was reported. All grade 3 or higher events occurred within the first two years after SABR.
The data are also supportive regarding kidney function. In FASTRACK II, the average decrease in renal function from baseline at month 12 was 10,8 mL/dk/1,73 m²and at month 24 it was 14,6 mL/dk/1,73 m² ; it then tended to plateau. This is particularly important for patients at high risk of dialysis after surgery or those who require a nephron-sparing approach.
The goal in kidney cancer is not simply to control the tumor. Preserving the patient's remaining kidney function is also very important. In some patients, surgery can cause a serious loss of kidney function or a risk of dialysis. SABR can provide local treatment in selected patients without removing kidney tissue; however, healthy kidney tissue must be carefully protected during radiotherapy planning.
Is SABR replacing surgery?
No. This point must be stated very clearly. FASTRACK II is a non-randomized phase 2 study conducted in patients who were unfit for surgery or at high surgical risk. It is therefore incorrect to say today that “SABR has replaced surgery.”
Surgery remains the main standard for localized kidney cancer, particularly in suitable patients. However, FASTRACK II strongly shows the following: in selected patients with primary kidney cancer for whom surgery cannot be performed, is very risky, or is declined, SABR should be seriously considered as a non-invasive and effective local treatment option.
| Clinical situation | Surgery | SABR | Comment |
|---|---|---|---|
| Localized RCC in a patient in good general health and fit for surgery | Standard approach | Should not replace surgery without a randomized comparison | Randomized studies of SABR vs surgery are needed in the future. |
| Medically inoperable patient | High risk or not possible | Strong non-invasive option | The most directly relevant target group of FASTRACK II. |
| Patient at high risk of dialysis after surgery | The risk of kidney function loss is important | May be a nephron-sparing alternative | Kidney function and tumor anatomy should be evaluated together. |
| Tumor in direct contact with the bowel | Technical surgical assessment is required | Was an exclusion criterion in FASTRACK II | Anatomical suitability is essential for SABR safety. |
| Tumor larger than 10 cm | Multidisciplinary assessment | FASTRACK II data cannot be directly generalized | Tumors larger than 10 cm were excluded from the study. |
Regulation and implementation: a matter of technique and center experience rather than a drug
SABR is not a drug; it is therefore not evaluated with the question “Does it have FDA approval?” as new molecules are. The real issues here are the place of the radiotherapy technique in guidelines, center infrastructure, team experience, the quality assurance program, and patient selection criteria.
According to the TROG statement, based on these results and other studies, SABR has become an option recommended in guidelines for patients with primary kidney cancer who do not undergo surgery. However, randomized studies are needed to compare SABR directly with surgery in patients who are fit for surgery.
How should this be explained to patients?
This treatment is not surgery; it involves delivering high-dose radiation to the tumor with great precision. Very high local control rates have been reported, especially in selected patients with kidney cancer who cannot undergo surgery or for whom surgery is very risky. However, it does not replace surgery for everyone. Tumor size, proximity to the bowel and other organs, kidney function, and the center's SABR experience should be evaluated together.
Critical reading: how should these data be interpreted in a balanced way?
Strong data, but from selected patients
- Local control is exceptionally strong: No local recurrence was reported in 70 patients during long-term FASTRACK II follow-up; 5-year local control in the pooled analysis was %98.
- No randomized comparison with surgery: It has not yet been established that SABR is equivalent to surgery in patients who are fit for surgery.
- Patient selection is critical: FASTRACK II data cannot be directly applied in situations such as eGFR <30, direct contact between the tumor and bowel, and tumors larger than 10 cm.
- Local control does not mean systemic control: The development of distant metastasis depends on tumor biology; systemic follow-up is needed even when local tumor control is excellent.
- Technical quality is very important: Motion management, image guidance, dose planning, and organ-at-risk constraints are fundamental components of success.
- Kidney function should be monitored: SABR may spare nephrons; however, healthy kidney tissue can be affected by radiation. eGFR should be monitored over the long term.
- Center experience is decisive: This treatment requires experienced radiation oncology and medical physics teams, as well as imaging infrastructure.
The message for practice in Türkiye
A substantial proportion of patients with kidney cancer in Türkiye can be treated with surgery; however, the group who are older, have a high cardiopulmonary risk, a solitary kidney, chronic kidney disease, or a risk of dialysis after surgery is not small. Active surveillance, ablation, systemic treatment, or palliative approaches are often discussed for these patients. FASTRACK II adds an option that is non-invasive, brief, and provides high local control for this patient group.
However, the decision to use SABR should not be made in isolation. Urology, radiation oncology, medical oncology, nephrology, interventional radiology, and radiology should assess the patient together. Tumor size, location, distance from the bowel, kidney function, the patient's life expectancy, and alternative treatment options should be discussed through a shared decision.
Drozdogan Academic Commentary
FASTRACK II is one of the most important studies changing our view of radiotherapy in primary kidney cancer. The old view that kidney cancer is “resistant to radiotherapy” is now largely losing its validity with modern SABR technology.
The absence of local recurrence during long-term follow-up after SABR delivered in 1 or 3 sessions to patients who are unfit for surgery or at high surgical risk makes this treatment a definitive option, meaning treatment with curative intent, for selected patients, beyond its palliative role.
However, this result does not mean that SABR will replace surgery in all patients. The main message is this: treatment options in primary kidney cancer no longer have to be confined to surgery and active surveillance. With the right patient, the right anatomy, strong technical infrastructure, and a multidisciplinary decision, SABR offers a very valuable third path, especially for patients who cannot undergo surgery.
Conclusion
FASTRACK II is a strong phase 2 study showing that SABR can provide very high local control in selected patients with primary renal cell cancer who do not undergo surgery. No local recurrence or death due to kidney cancer was reported in the long-term FASTRACK II data from 70 patients. In the pooled FASTRACK + FASTRACK II analysis of 103 patients, 5-year local control was reported as %98.
Treatment can be delivered in only 1 or 3 sessions; it does not require anesthesia, an incision, or surgical removal of an organ. Although the safety profile appears acceptable, proximity to the bowel, kidney function, and technical planning are critically important.
The most appropriate clinical interpretation is this: SABR is a strong, non-invasive, brief treatment option with nephron-sparing potential for patients with primary kidney cancer who are unfit for surgery or at high surgical risk. However, randomized studies comparing it with surgery should be awaited before changing the standard approach for patients who are fit for surgery.
- TROG Cancer Research. FASTRACK II trial finds emerging radiotherapy technique effectively controls kidney cancer. 18 May 2026.
- Siva S et al. Stereotactic ablative body radiotherapy for primary kidney cancer (TROG 15.03 FASTRACK II): a non-randomised phase 2 trial. Lancet Oncology. 2024.
- Siva S et al. Long-term outcomes of stereotactic ablative body radiotherapy for primary kidney cancer: final FASTRACK II results. Lancet Oncology. 2026.
- Siva S et al. Five-year outcomes from pooled FASTRACK and FASTRACK II data. Lancet Oncology. 2026.
- OncoDaily. Long-Term FASTRACK II Data Support SABR for Primary Kidney Cancer. 17 May 2026.
- The ASCO Post. SABR for Patients With Primary Kidney Cancer Not Undergoing Resection. 18 March 2024.
- eviQ. Renal cell carcinoma definitive stereotactic EBRT protocol.
- ClinicalTrials.gov. FASTRACK II / NCT02613819.
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