Stereotactic Ablative Radiation for Systemic Therapy-naïve Oligometastatic Kidney Cancer

BACKGROUND: Evidence-based guidelines for the management of systemic therapy-naïve oligometastatic renal cell carcinoma (RCC) are lacking. OBJECTIVE: To evaluate the potential of stereotactic ablative radiotherapy (SAbR) to provide longitudinal disease control while preserving quality of life (QOL) in patients with systemic therapy-naïve oligometastatic RCC. DESIGN, SETTING, AND PARTICIPANTS: RCC patients with three or fewer extracranial metastases were eligible. SAbR was administered longitudinally to all upfront and, as applicable, subsequent metastases. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: This prospective phase II single-arm trial was powered to achieve a primary objective of freedom from systemic therapy for >1 yr in >60% of patients (using the Clopper and Pearson methodology). Secondary endpoints included progression-free survival (PFS), defined as the time from first SAbR to progression not amenable to SAbR (local failure at SAbR-treated sites, new metastases not amenable to SAbR, more than three new metastases, or brain metastases); patient-reported QOL metrics; local control (LC) rates; toxicity; cancer-specific survival (CSS); and overall survival (OS). RESULTS AND LIMITATIONS: Twenty-three patients received SAbR to 33 initial and 57 total sites. The median follow-up was 21.7 mo (interquartile range 16.3-30.3). Exceeding the prespecified 60% benchmark, freedom from systemic therapy at 1 yr was 91.3% (95% confidence interval [CI]: 69.5, 97.8). One-year PFS was 82.6% (95% CI: 60.1, 93.1). QOL was largely unaffected. LC was 100%. There were no grade 3/4 toxicities, but there was one death due to immune-related colitis 3 mo after SAbR while on subsequent checkpoint inhibitor therapy, where a SAbR contribution could not be excluded. One-year OS was 95.7% (95% CI: 72.9, 99.4); one-year CSS was 100%. CONCLUSIONS: SAbR for oligometastatic RCC was associated with meaningful longitudinal disease control while preserving QOL. These data support further evaluation of SAbR for systemic therapy-naïve oligometastatic RCC. PATIENT SUMMARY: Sequential stereotactic radiation therapy can safely and effectively control metastatic kidney cancer with limited spread for over a year without compromising patients' quality of life.