Baseline Clinical Characteristics
A total of 6070 patients aged ≥65 years who had been diagnosed with stage IB NSCLC were included in our study (cohort 1). Univariate Cox analysis showed that the OS of the patients was related to race, gender, marital status, tumor size, pleural invasion, tumor grade, tumor classification, surgery, lymphadenectomy, and radiation (Figure S1A). Further multivariate Cox analysis showed that race, gender, marital status, tumor size, tumor classification, and surgery were the independent predictive factors for OS (Figure S1B). Analogously, the DSS of the patients was associated with gender, marital status, tumor size, pleural invasion, tumor grade, tumor classification, surgery, and lymphadenectomy in Univariate Cox analysis (Figure S1C). Gender, tumor size, tumor classification, surgery, and lymphadenectomy were the independent predictive factors for DSS (Figure S1D). Remarkably, surgical treatment was the most significant protective factor for both OS and DSS.
The K-M curves showed that the OS and DSS of patients aged ≥65 years with stage IB NSCLS who underwent surgery were significantly better than those who did not undergo surgery (P < 0.001, both; Figure S2). Of the population surveyed, about 71.50% of patients (4340 patients) underwent surgical resection. The baseline clinical characteristics of the patients are shown in Table 1. The results showed that the distribution frequencies of some general characteristics, such as race (P < 0.001), gender (P = 0.003), and marital status (P < 0.001) were unbalanced between the surgery and no surgery groups. In terms of tumor pathological characteristics, the surgery group was associated with larger tumor size (P < 0.001), location of the right lung (P < 0.001), positive pleural invasion (P < 0.001), more classification of adenocarcinoma (P < 0.001), and moderate tumor grade (P < 0.001). In terms of therapy, the patients in the surgery group were more likely to have received lymphadenectomy (P < 0.001) and not received radiotherapy (P < 0.001). However, chemotherapy (P = 0.309) was not significantly different between the two groups. Given the unbalanced distribution of these indicators between the surgical and non-surgical groups, the interference from these factors needs to be minimized to determine the significance of surgery for prognosis.
Survival analysis and multivariate Cox analysis after Propensity Score Matching
After 1:1 PSM of 11 clinical characteristics, a total of 361 pairs of patients were included in the surgery group and the no surgery group (cohort 2), respectively. The distribution of baseline characteristics was almost balanced between the two groups (P > 0.1) (Table 2).
After PSM, univariate Cox analysis showed that gender (P = 0.005), tumor classification (P = 0.012), and surgery (P < 0.001) were the prognostic factors for OS, whereas only surgery (P < 0.001) was the prognostic factor for DSS (Figure 2A and 2C). The results of subsequent multivariate analysis showed that gender (P = 0.007), tumor classification (P = 0.001), surgery (P < 0.001), and radiation (P = 0.044) for OS; as well as tumor classification (P = 0.043) and surgery (P < 0.001) for DSS were the independent predictive factors (Figure 2B and 2D).
Kaplan-Meier survival analysis after PSM showed that the OS of the surgery group was significantly better than that of the no-surgery group (P < 0.001). The median OS time of the surgery group was 61 months, which was significantly longer than the median OS time of the no-surgery group (22 months) (Figure 3A). Similar to the OS, the DSS of patients in the surgery group was also significantly better than that of patients in the no surgery group (P < 0.001), with the median DSS being 71 months in the surgery group and 29 months in the no surgery group (Figure 3B).
Subgroup Analysis of OS and DSS in Subgroups of Clinical Characteristics
To better compare the protective effect of surgical factors on prognosis after PSM and to further reduce the interference of other factors on the outcome, subgroup analyses of all clinical characteristics were performed. The OS subgroup analysis showed that surgery was a protective prognostic factor for OS in almost all subgroups of clinical characteristics (Figure 4). In some subgroups of clinical characteristics, such as the Black subgroup in the race, the large cell carcinoma subgroup in tumor classification, and the unknown subgroup in lymphadenectomy, the difference in OS between surgery and no surgery patients was statistically insignificant because of the small number of cases. The DSS subgroup analysis also showed that surgical treatment was a protective factor for DSS survival in all subgroups with a patient sample size > 100 (Figure 5).
Prognostic Factors of Patients in the Surgery Group
To further investigate the prognostic factors of older patients with IB stage NSCLC undergoing surgery, we screened the clinical characteristics of these patients in the surgery group using multivariate Cox analysis. The results showed that gender (male vs. female), tumor size (larger tumor size), tumor grade (lower grade), and tumor type (other pathological types vs. adenocarcinoma) were the statistically negative influencing factors for OS and DSS in the surgery group. In addition, race (other ethnicity vs. White) was also a negative prognostic factor for OS (Figure 6A), but not for DSS (Figure 6B).