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High-dose, high-precision radiation may be as safe and effective for renal cell carcinoma (RCC) patients with a single kidney as it is for those with both, according to an analysis of the IROCK consortium.

Renal stereotactic ablative radiotherapy (SABR) demonstrated similar rates of local control (HR 0.89, P=0.923), cancer-specific survival (HR 0.16, P=0.082), and overall survival (HR 0.75, P=0.445) in solitary and bilateral cohorts, reported Rohann Correa, MD, PhD, of the London Health Sciences Centre in London, Ontario, Canada.

The 2-year local control and cancer-specific survival rates were 98% for single kidney patients treated with SABR, and just a 1% difference was observed in overall survival between patients with one or both of their kidneys (81% versus 82%, respectively).

SABR, or stereotactic radiation therapy (SBRT), slightly affected renal function in patients with a single kidney, compared to those with both (P=0.984). Specifically, the solitary kidney cohort averaged a decrease in estimated glomerular filtration rate (eGFR) of -5.8 (±10.8 mL/min) while the bilateral cohort averaged a decrease of -5.3 (±14.3 mL/min), Correa reported here at the American Society for Radiation Oncology (ASTRO) annual meeting.

However, these results may depend on the severity of the cancer case at hand. In this study, pre-existing moderate chronic kidney disease (eGFR ≤60 mL/min) in patients with a single kidney was associated with poorer progression-free survival (HR 2.66, P=0.043). And after patients were treated with SABR, decreased eGFR was more frequently observed in those with larger tumors at onset (HR 4.2, P=0.029).

"Solitary kidney RCC represents a unique situation and challenging management scenario, partly because of patient factors," Correa said. "The current management options for patients with solitary kidney RCC tend to be somewhat invasive, either requiring surgical or percutaneous access and are limited to size and location. SABR, on the other hand, is a non-invasive outpatient strategy requiring a single or few visits."

The standard treatment for RCC is surgery or tumor ablation for those who are ineligible. While SABR has demonstrated efficacy in treating lung and liver cancers, among others, it recently demonstrated success in treating RCC. However, it was unclear whether these results would prevail in patients with just one kidney.

"The local control was extraordinarily good with SBRT," Howard Sandler, MD, of Cedars-Sinai Medical Center in Los Angeles, told 番茄社区app. "These kidney tumors were nearly all completely controlled, and while nothing is ever 100% safe in medicine, the treatment seemed very well tolerated."

Sandler said that while no one would dispute that surgery is the main treatment for kidney cancer in this setting, the idea that radiation oncologists can treat RCC is paradigm changing. He noted that as the kidney is one of the organs known to be sensitive to radiation, the concern has been whether in killing the cancer, the kidney would be damaged to the point that a patient would require dialysis.

"That didn't happen," he said. "They did notice that the kidney function went down, but depending on where people start, most people can tolerate the drop."

Sandler said the researchers found "a small, tolerable, acceptable amount of kidney injury, and at the same time they got 98% tumor control."

Correa said these results may eventually lead to this new treatment method replacing surgery, but that since this was a retrospective study, more studies that directly compare the two treatment options are needed.

"I don't think we are ready yet for replacement to be in the discussion, but I think for the right patient, this should be an option worthy of consideration," he said.

This study collected patient data from nine institutions in the International Radiosurgery Oncology Consortium for Kidney (IROCK) group across the U.S., Germany, Australia, Canada, and Japan. From this data, 81 patients with a solitary kidney underwent SABR. The patients were 67.5 years of age, on average, were mostly men (69%), and nearly all (97.5%) had an ECOG 0-1 performance status. Patients were followed an average of 2.6 years.

Patients with solitary kidneys had an average tumor size of 3.7 cm, while those with bilateral kidneys had an average tumor size of 4.3 cm (P<0.001). Single kidney patients demonstrated higher baseline kidney function (64.6 ± 21.7 mL/min) compared to those with both kidneys (57.2 ± 21.6 mL/min, P=0.016). None of the patients with one kidney required dialysis, while six (4.2%) of the patients with both kidneys did.

Treatment included an average 25 Gy dose in one fraction. And while both total dose and number of fractions were significantly lower in the solitary cohort than in the bilateral cohort (P≤0.001), the average biologically effective dose of radiation therapy was 87.5 Gy in both groups (P=0.103).

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