medwireNews: Stereotactic ablative body radiotherapy (SABR) has high local efficacy and minimal impact on renal function in the long term among people with localized renal cell carcinoma (RCC), say researchers who conducted an individual patient data meta-analysis of the IROCK database.
Noting that the cohort was “predominantly medically inoperable,” they say “[t]hese mature data lend further support for renal SABR as a treatment option for patients unwilling or unfit to undergo surgery.”
The study included data on 190 patients who received SABR for primary nonmetastatic RCC at one of 12 institutions in five countries between March 2007 and September 2018. Patients were aged a median of 73.6 years and the majority were men (73%) and unable to undergo surgery (75%). The median tumor size was 4 cm and the median follow-up was 5.0 years.
As reported in The Lancet Oncology, the cumulative incidence of local failure with death as a competing risk was an identical 5.5% at 3 and 5 years, rising to 8.4% at 7 years.
The cumulative incidence of distant failure at these timepoints was 8.4%, 10.8%, and 15.0%, respectively, with rates for any failure of 10.6%, 13.0%, and 18.8%.
The researchers report that the estimated cancer-specific survival (CSS) rates at 3, 5, and 7 years were 95.5%, 92.0%, and 92.0%, respectively, while the progression-free survival (PFS) rates were 72.1%, 63.6%, and 48.5%. The median CSS and PFS durations were unreached and 6.7 years, respectively.
Interestingly, the 43% of patients who received single-fraction SABR appeared to have significantly better local control and PFS, but not CSS, than the 57% who received multifraction SABR.
This observation was confirmed in a multivariable analysis adjusting for factors such as age, performance status, and maximum tumor dimension, which showed a significant 6.10-fold higher risk for local failure with multifraction versus single-fraction SABR.
Shankar Siva (Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia) and co-investigators note that “[t]his finding is consistent with a previous report in oligometastatic renal cell carcinoma,” but stress that the comparison between single-fraction and multifraction SABR should be considered hypothesis-generating.
They continue: “[F]urther evidence from randomised trials is needed to elucidate optimal treatment schedules.”
The researchers also evaluated the impact of SABR on renal function, finding that in the overall cohort the estimated glomerular filtration rate decreased by a median of 10.3 mL/min per 1.73 m2 at 3 years and 14.2 mL/min per 1.73 m2 at 5 years from a baseline value of 60.0 mL/min per 1.73 m2, which they describe as “a clinically acceptable decline.”
Seven patients (4%), two of whom had a solitary kidney, required dialysis after SABR.
With regard to the safety of SABR, 37% of patients experienced an adverse event of grade 1 or 2, and one patient each developed a treatment-related grade 4 duodenal ulcer and grade 4 gastritis. There were no grade 3 events nor treatment-related deaths.
The author of a related commentary says that “although this report was retrospective and a large variety of dose-fractionation protocols were used for SABR, these findings are important because they demonstrate the long-term efficacy and safety of SABR for primary renal cell carcinoma based on multicentre data.”
Takashi Mizowaki, from Kyoto University in Japan, continues: “Furthermore, as options for radical therapy are extremely limited for primary renal cell carcinoma in patients ineligible for surgery with tumour diameters greater than 4 cm, I believe this report contributes to the future expansion of SABR application to renal cell carcinoma.”
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