Abstract： Objective:To investigate the effect of spread through air spaces (STAS) on the postoperative prognosis of patients with stage pT1N0M0 lung adenocarcinoma according to different tumor sizes.Methods:The clinicopathological and follow-up data of 511 patients with pT1N0M0 lung adenocarcinoma treated surgically in the Department of Thoracic Surgery, Cancer Hospital, Chinese Academy of Medical Sciences from January 2014 to June 2018 were retrospectively analyzed. There were 285 males and 226 females, aged 60 (53, 66) years. Those patients were divided into two groups according to STAS status, including STAS (-) group (342 cases) and STAS (+) group (169 cases). And the stratified analysis was performed according to the American Cancer Consortium (AJCC) 8th edition postoperative pathological tumor size T-stage (pT) of lung cancer, which was divided into pT1a (pT≤1 cm, 93 cases), pT1b (1 cm<pT≤2 cm, 280 cases), pT1c group (2 cm<pT≤3 cm, 138 cases) and pT1b/c (1 cm<pT≤3 cm, 418 cases). Univariate and multivariate Cox regression analyses and inverse probability weighted (IPTW) adjusted Kaplan-Meier (K-M) curves were used to analyze the effect of STAS on recurrence-free survival (RFS) in patients included in this study.Results:The recurrence rate was significantly higher in the STAS (+) group compared to the STAS (-) group (22.5% vs 3.2%, P<0.001). Multifactorial Cox regression analysis based on pT stratification showed that the risks of recurrence were 4.56-fold (95% CI:1.56-13.33; P=0.006) and 3.16-fold (95% CI:1.07-9.33; P=0.038) higher in pT1b and pT1c staged patients with STAS (+) than in STAS (-) patients, respectively. There was no significant difference in RFS between the STAS (-) group of pT1b/c, pT1b and pT1c and all pT1a patients [(84.97±0.72) vs (84.05±1.11) months, (85.60±0.74) vs (84.05±1.11) months, (81.49±1.63) vs (84.05±1.11) months; all P>0.05]. Before and after IPTW adjustment, statistically significant differences were found in RFS between STAS (+) group and STAS (-) group [(72.50±2.23) vs (85.12±0.72) months, (77.74±1.12) vs (84.59±0.64) months, all P<0.001]. In addition, the risks of both local and distant recurrence were higher in STAS (+) group compared to STAS (-) group (6.7% vs 1.2% and 8.2% vs 3.6%, respectively; both P<0.05). Conclusion:For lung adenocarcinoma patients with pT1bN0M0 and pT1cN0M0, those patients with STAS (+) had a higher incidence of both local and distant recurrence and with poor RFS.