Efficacy of Stereotactic Ablative Body Radiotherapy (SABR) in uncommon subtypes of primary kidney cancer: An analysis from the International Radiosurgery Oncology Consortium of the Kidney

Abstract

Background: While stereotactic ablative body radiotherapy (SABR) is associated with excellent local control for primary renal cell carcinoma (RCC), outcomes based on clear-cell (ccRCC) and non-clear cell (nccRCC) histologies are not well defined.

Methods and materials: Individual data of adult patient with biopsy confirmed primary RCC receiving SABR between 2007 and 2021 from 16 institutions in Australia, Canda, Germany, Japan and USA pooled. Patients with metastatic disease or upper tract urothelial carcinoma were excluded. The primary outcome was local failure (LF), based on the Response Evaluation Criteria in Solid Tumours (RECIST) version 1.1. Distant failure (DF), cancer-specific survival (CSS), treatment related toxicity and renal function changes following SABR were defined as secondary outcomes. Kaplan-Meier estimates were generated for LF, DF and CSS stratified by clear cell vs. non-clear cell histology, compared using the log-rank test (CSS) or Gray's test (LF and DF).

Results: Two hundred and eleven patients with a biopsy confirmed ccRCC (n=167) or nccRCC (n=44) were included. In the nccRCC group, 59% (n=26/44) and 11% (n=5/44) were papillary and chromophobe histologies, respectively. Patients with nccRCC were more likely to be older (median age at SABR 77.2 years vs. 71.5, p=0.009) and to be treated with multifraction SABR (82% [n=36/44] vs. 38% [n=63/167]; p < 0.001) than the ccRCC group. The median follow-up was 4.02 years (IQR: 3.43-4.94) and 4.25 years (IQR: 3.02-5.00) for ccRCC and nccRCC groups, respectively. The 5-year cumulative incidence of LF was 1.5% (95% confidence interval [CI]: 0.3-4.8%) in ccRCC group vs. 2.4% (95% CI: 0.2-11.0%) in nccRCC group (hazard ratio [HR]: 0.90, 95% CI: 0.10-8.31, p=0.922). The corresponding cumulative incidence of DF at 5-years was 6.0% in ccRCC group vs. 2.9% in nccRCC group (HR: 0.34, 95% CI: 0.04-2.68, p=0.304). The 5-year estimated CSS was 96.4% in ccRCC group vs. 96.4% in nccRCC group (HR: 2.04, p=0.561). From baseline, eGFR reduced by 11.4 ± 13.4 mL/min at 3 years and by 12.2 ± 14.0 mL/min at 5 years. Sixteen patients (7.6%) experienced grade-2 or higher toxicities, with grade-2 fatigue (5.7%) being the most common.

Conclusion: SABR provides excellent oncologic outcomes, irrespective of ccRCC or nccRCC histology.

Keywords: Papillary and chromophobe RCC; Renal cell carcinoma; SABR; Stereotactic ablative radiotherapy; clear-cell RCC; non-clear cell RCC; survival; toxicity.