Impact of lung parenchymal-only failure on overall survival in early stage lung cancer patients treated with stereotactic ablative radiation therapy

Abstract Introduction The impact of lung parenchymal-only failure on patient survival after stereotactic ablative body radiotherapy (SABR) for early stage non-small cell lung cancer (NSCLC) remains unclear. Methods The study population included 481 patients with early stage NSC LC who were treated with 3 to 5 fraction SABR between 2000 and 2016. The primary study objective was to assess the impact of out-of-field lung parenchymal-only failure (OLPF) on overall survival (OS). Results At a median follow-up of 5.9 years, the median OS was 2.7 years for all patients. Patients with (OLPF) did not have a significantly different OS compared to patients who never failed (p=0.0952, median OS 4.1 years with failure vs. 2.6 years never failure). Analysis in a 1:1 propensity score-matched cohort for KPS, co-morbidity score, and smoking status showed no differences in OS between patients that never failed and those with OLPF (p=0.8). In subgroup analyses exploring impact of time of failure on OS, patients with OLPF 6 months or more after diagnosis did not have significantly different OS compared to those who never failed, when accounting for immortal time bias (p= 0.3, median OS 4.3 years vs 3.5 years never failure). Only seven patients in our dataset failed within 6 months of treatment, of which only four were confirmed to be true failures; therefore, limited data is available in our cohort on the impact of OLPF in ≤6 months on OS. Conclusions OLPF after SABR for early stage NSCLC does not appear to adversely affect OS, especially if occurring at least 6 months after SABR. More studies are needed to understand if OLPF within 6 months of SABR is associated with adverse OS. These data are useful when discussing prognosis of lung parenchymal failures after initial SABR.