Objective  To retrospectively analyze the correlation between the International Association for the Study of Lung Cancer (IASLC) grading system and clinicopathological features of stage I invasive non-mucinous lung adenocarcinoma, and its impact on the prognosis of the patients.

  Methods  The clinicopathological and follow-up data of 204 patients with stage I invasive non-mucinous lung adenocarcinoma, who were enrolled in Tianjin Chest Hospital from January 2015 to December 2018, was collected and analyzed. The patients were assigned into groups according to the IASLC grading system. One-way ANOVA, the Chi-square test, and the Fisher's exact test were used to analyze the correlation between the IASLC grading system, and the clinicopathological characteristics of stage I invasive non-mucinous lung adenocarcinoma, and the impact of the IASLC grading system on the prognosis and recurrence of patients with invasive non-mucinous lung adenocarcinoma. The overall survival (OS) rate and recurrence-free survival (RFS) rate of patients with invasive non-mucinous lung adenocarcinoma was calculated using the Kaplan–Meier method. The Log-rank test was used to compare the differences between different groups. Independent risk factors were analyzed using univariate and multivariate Cox regressions.

  Results  Of the 204 patients with stage Ⅰ invasive non-mucinous lung adenocarcinoma, 108 were grade Ⅰ; 66, grade Ⅱ; and 30, grade Ⅲ tumors. IASLC grade was significantly correlated with sex (P=0.022), smoking history (P=0.041), vascular invasion (P=0.004), pleural involvement (P=0.001), pathological stage (P<0.001), and tumor diameter (P<0.001). Results from the univariate survival analysis showed that the pleural involvement (P=0.043) and IASLC grade (P<0.001) had significant effects on OS, while the IASLC grade had a significant impact on RFS (P<0.001). Moreover, multivariate Cox regression analysis showed that tumor diameter (P=0.005) and IASLC grade (P=0.002) were independent risk factors for OS of patients with stage I invasive non-mucinous lung adenocarcinoma, while the tumor diameter (P=0.007) and IASLC grade (P=0.003) were independent factors for recurrence in patients with stage I invasive non-mucinous lung adenocarcinoma.

  Conclusions  The IASLC grading system is an independent prognostic factor for stage I invasive non-mucinous lung adenocarcinoma. The higher the IASLC grade, the worse the prognosis of patients with stage I invasive non-mucinous lung adenocarcinoma. The grading system provides a new prognostic grouping method and a new approach to postoperative management and treatment of patients with stage I invasive non-mucinous lung adenocarcinoma.