A groundbreaking study presented at the American Society for Radiation Oncology (ASTRO) annual meeting revealed that Stereotactic Ablative Body Radiotherapy (SABR) is proving to be an effective and noninvasive alternative treatment for primary renal cell carcinoma (RCC) patients who are not suitable candidates for surgery. The FASTRACK II trial, a prospective phase II study involving 70 patients, demonstrated incredibly promising results. Over the duration of the trial (median follow-up of 43 months), no patient experienced local progression of kidney cancer, and cancer-specific survival stood at an impressive 100%. These outcomes highlight the potential of SABR as a new standard of care for primary kidney cancer patients not suited to undergo surgery.
The incidence rate of renal cell carcinoma has been on the rise worldwide over the past three decades, with a significant increase observed in individuals aged 70 and older. While surgery, such as total or partial nephrectomy, is currently considered the standard of care, there are limitations for medically inoperable patients or those at high risk, such as the possibility of post-surgical dialysis. This is where SABR comes into play, offering a potential solution for patients in these situations.
SABR, also known as Stereotactic Body Radiotherapy (SBRT), presents several advantages over traditional treatment options for primary kidney cancer. First and foremost, SABR is a noninvasive procedure that eliminates the need for general anesthesia. Additionally, it has the ability to treat perihilar and large tumors that cannot be effectively addressed through thermal ablation. This breakthrough technology opens up new possibilities for patients who would otherwise have limited treatment options.
The TROG 15.03/ANZUP international multicenter FASTRACK II trial, conducted between July 2016 and February 2020, included seven Australian centers and one Dutch center. The trial enrolled patients with a biopsy-confirmed diagnosis of primary RCC and a single lesion within a kidney. To be eligible, patients needed to have an ECOG performance score of 2 or less, an estimated glomerular filtration rate (eGFR) greater than 30 mLs/min, and be medically inoperable, at high risk, or unwilling to undergo surgery.
The median age of the patients was 77, with 70% being male. The median BMI was 32, and the median Charlson comorbidity score stood at 7. Around one-third of patients had T1a disease, which could potentially be addressed through thermal ablation. The majority of patients (56%) had T1b disease or greater. Patients with tumors measuring less than or equal to 4 cm received a single fraction of 26 Gy, while those with tumors larger than 4 cm were prescribed 42 Gy in three fractions.
Despite the larger tumor size observed in this trial compared to other studies investigating partial nephrectomy versus radical nephrectomy, SABR proved to be equally effective in maintaining renal function. The baseline mean eGFR was 61.1 mLs/min and only decreased by -10.8 mLs/min after 1 year. The decline in eGFR continued at a slower rate over time, reaching -14.6 mLs/min after 2 years and then plateauing. Interestingly, only one patient required dialysis.
The safety profile of SABR in the FASTRACK II trial was excellent, with no reported grade 4 or 5 treatment-related adverse events (TRAEs). Only 10% of patients experienced grade 3 TRAEs, most of which were transient pain or nausea and vomiting. Although prophylactic antiemetics or steroids were not mandatory in this trial, it is recommended that they be considered in future treatments to further minimize these side effects for patients.
The FASTRACK II trial results provide compelling evidence that SABR is a highly effective and noninvasive treatment option for primary renal cell carcinoma patients not eligible for surgery. The study outcomes strongly support the design of a future randomized clinical trial comparing SABR to surgery for primary kidney cancer. As researchers continue to explore and refine the use of SABR in oncology, this breakthrough technology has the potential to revolutionize the management of primary kidney cancer, offering hope and improved outcomes for a growing patient population.