Lung cancer patients may have treatment delays due to the 2019 coronavirus disease (COVID-19) pandemic. The researchers aimed to determine how much longer delays in treating stage III-IV non-small-cell lung cancer affected survival. Cox regression analysis with penalized smoothing splines was used to analyze data from the National Lung Screening Trial (NLST) and the National Cancer DataBase (NCDB) to determine if there was a correlation between the length of time between diagnosis and treatment and the risk of death from any cause for patients with stage III or stage IV lung cancer. To evaluate whether patients who started therapy sooner or later fared better, the NCDB employed a propensity score-matched study (ie, 0-30 vs. 90-120 days following diagnosis). A decrease in hazard ratio was observed in the NLST (n=392) and NCDB (n=275,198) cohorts using Cox regression analysis, suggesting that the longer treatment was postponed, the better. There were no statistically significant differences in survival between early and delayed treatment for patients with stage IIIA, IIIB (T3-4,N2,M0), IIIC, and IV (M1B-C) adenocarcinoma and stage IIIA, IIIB, IIIC, and IV (M1B-C) squamous cell carcinoma (all log-rank P>.05) in a propensity score-matched analysis. It was found that delaying treatment enhanced survival for patients with stage IIIB (T1-2,N3,M0) and stage IV (M1A) adenocarcinoma (log-rank P=.03, P=.02). Despite taking wait time bias into account, the results of the sensitivity study remained unchanged.