Abstract
Purpose: While SABR is associated with excellent local control of primary renal cell carcinoma (RCC), outcomes based on clear cell RCC (ccRCC) and non-clear cell RCC (nccRCC) histologies are not well defined. This retropsective study's objective is to report the outcomes following SABR for uncommon subtypes of primary RCC.
Methods and materials: Individual data of adult patients with biopsy-confirmed primary RCC receiving SABR between 2007 and 2021 from 16 institutions in Australia, Canada, Germany, Japan, and the USA were 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 Tumors 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 ccRCC versus nccRCC histology, and compared using the log-rank test (for CSS) or Gray's test (for LF and DF).
Results: Two hundred 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 = .009) and to be treated with multifraction SABR (82% [n = 36/44] vs 38% [n = 63/167]; p < .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 the ccRCC and nccRCC groups, respectively. The 5-year cumulative incidence of LF was 1.5% (95% CI, 0.3%-4.8%) in the ccRCC group versus 2.4% (95% CI, 0.2%-11.0%) in the nccRCC group (hazard ratio [HR], 0.90; 95% CI, 0.10-8.31; p = .922). The corresponding cumulative incidence of DF at 5 years was 6.0% in the ccRCC group versus 2.9% in the nccRCC group (HR, 0.34; 95% CI, 0.04-2.68; p = .304). The 5-year estimated CSS was 96.4% in the ccRCC group versus 96.4% in the nccRCC group (HR, 2.04; p = .561). From baseline, the mean ± SD estimated glomerular filtration rate 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.
Conclusions: SABR provides excellent oncologic outcomes, irrespective of ccRCC or nccRCC histology.
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