Ablative RT could be alternative for solitary-kidney RCC

Stereotactic ablative body radiotherapy (SABR) for renal cell carcinoma (RCC) in patients with a solitary kidney provides excellent local oncologic control with acceptable impact on renal function, according to findings from an individual-patient pooled analysis from the International Radiosurgery Oncology Consortium for Kidney (IROCK).

The research was reported by Rohann Correa, MD, PhD, at the American Society for Radiation Oncology annual meeting in San Antonio.

“Solitary kidney RCC represents a challenging management scenario because these patients lack renal function reserve, putting them at high risk for renal dysfunction. SABR is an emerging non-invasive treatment for RCC that, by delivering a high dose of radiation per fraction, is thought to have the potential to overcome RCC resistance to standard-fractionation radiotherapy,” said Dr. Correa, of London Health Sciences Center, London, Ontario, Canada, working with Alexander Louie, MD, PhD, and colleagues.

Read: Could BMI predict mRCC treatment outcomes?

“Our encouraging data support further study of SABR as an alternative treatment modality for RCC, particularly in the high-risk setting of solitary kidney disease, and particularly for patients who are poor candidates for operative or interventional management for reasons of medical comorbidity or tumor size and/or location. We believe that referral for kidney SABR is worthy of consideration in patients with solitary-kidney RCC who are faced with limited and risky management options,” he told Urology Times.

To investigate SABR as a definitive treatment option in patients with solitary kidney RCC, Dr. Correa and colleagues conducted a retrospective study analyzing individual patient data submitted from the nine IROCK centers worldwide. Patients with RCC histology and serial enlargement demonstrated on multiple imaging sets who were treated with one to 10 fractions of SABR and who had at least 1-year of follow-up were included.

The pooled cohort included 223 patients, of whom 81 had a functionally or anatomically solitary kidney. The solitary kidney subgroup had a mean age of 67 years and were predominantly male (69%) with good performance status (97.5%). Mean estimated glomerular filtration rate (eGFR) was 64.6 mL/min, indicative of slightly worse than mild renal dysfunction.

Mean maximum dimension tumor size was 3.5 cm, and the median biologically effective dose of radiation given was 87.5 Gy. The majority of solitary kidney patients (84%) were treated with single-fraction SABR, although multi-fraction treatments were also utilized (range, 1-10) with a median fractional dose of 25 Gy (range, 6-26 Gy).

The subset of remaining patients who had bilateral functioning kidneys were slightly older on average, had slightly lower mean eGFR and larger tumors, and included a lower percentage of patients with good performance status, but received a similar radiation dose, Dr. Correa noted.

Next: eGFR decreased modestly in both the solitary kidney and bilateral kidney subgroupsAfter median follow-up of 2.6 years, eGFR decreased modestly in both the solitary kidney and bilateral kidney subgroups, –5.8 mL/min and –5.3 mL/min, respectively. The change, which represented a decline of about 9% from baseline in each group, was not significantly different between groups. There was, however, a trend for more patients in the bilateral group to need dialysis (0 vs. 6 patients, respectively; p=.089).

Dr. Correa reported that in a univariable logistic regression analysis conducted to identify factors predicting a decrease in eGFR ≥15 mL/min, tumor diameter ≥4.0 cm was the only associated variable (OR: 4.21, 95% CI: 1.16-15.31, p=.029).

“Given this finding, caution is indicated when treating larger tumors in this setting,” Dr. Correa said.

Also see: Tool differentiates renal oncocytoma, chromophobe RCC

Data on oncologic outcomes showed local recurrence occurred in a single patient in the solitary kidney subgroup and in two patients in the bilateral group. Cancer-specific survival was excellent in both groups, but the rate was significantly higher in the solitary subgroup than in patients with two functioning kidneys (98.2% vs. 94.3%; p=.047); there was no significant difference in the overall survival rate between the solitary and bilateral subgroups (81.5% vs. 82.4%; p=.356).

Going forward, Dr. Correa and colleagues are exploring comparative effectiveness research that will compare SABR with other available modalities for RCC (ie, surgery or thermal ablation).