High Risk Prognostic Factors Predictive of Outcome Following Stereotactic Body Radiation Therapy (SBRT) for Early-Stage Lung Cancer

Abstract

High risk prognostic factors for outcomes following SBRT for early-stage lung cancer per SWOG/NRG 1914 include: tumor size > 2cm; moderately/poorly/undifferentiated histology; or high metabolic activity on PET/CT defined as SUV > 6.2. The purpose of this IRB approved retrospective study is to assess outcome for stage I lung cancer and to validate SWOG risk stratification in a single community-based radiation department. A total of 132 patients with 139 tumors treated with SBRT between 2014 and 2019 were stratified by SWOG risk group (high vs. low). To assess differences by risk group in estimated overall survival (OS) at the patient level, as well as Freedom from Local Failure (FFLF), Freedom from Regional Failure (FFRF) and Freedom from Distant Failure (FFDF) at the tumor level, Kaplan-Meier methodology and Cox proportional hazards (PH) modeling for correlated data were used. Statistical significance was concluded at the 0.05 level. Median follow-up for the entire group is 56 months. 77% of patients had high risk tumors. The median patient age was 75 years with 57% female. Patients with high-risk tumors were older (p = 0.023) compared to patients with low-risk tumors. At the tumor level, high risk tumors were more likely to have biopsies performed (91% vs 57% p = 0.002) and more likely to experience regional failure (28% vs 7% p = 0.005). High risk tumors were more likely to experience local failure (8% vs 0% p = NS) and distant failure (27% vs 14% p = NS). Median survival was 49 months for the whole group (46.0 months high risk, 65.1 months low risk). Actuarial OS at 5 years is 38% (35% high risk, 51% low risk). Actuarial FFLF at 5 years is 94% (93% high risk, 100% low risk). Actuarial FFRF at 5 years is 77% (72% high risk, 93% low risk). Actuarial FFDF at 5 years is 74% (70% high risk, 88% low risk). Cox PH models revealed no statistically significant differences in FFRF by risk group (p = 0.08). Excellent local control but higher regional and distant failure was demonstrated for high-risk lung tumors as defined by SWOG/NRG 1914. Clinically important decrement in outcomes were consistently noted for high-risk tumors in this sample which did not demonstrate statistical significance due to lack of events and statistical power. However, our data supports the prognostic importance of tumor size/grade and SUV for identifying patients at high risk. Further validation with larger sample sizes would contribute to our knowledge regarding risk stratification for early-stage lung cancer treated with SBRT.