Clinicopathologic comparison of surgical approaches

In Table 1, the characteristics of 564 surgically removed lung adenocarcinomas that are 2 cm or smaller are shown, categorized by type of surgery, with 266 lobar resections and 298 sublobar resections. Most patients in our study were female (61%), with a median age of 56. Tumors that underwent sublobar resection were typically 3 mm smaller compared to those that underwent lobar resection. AAH/AIS/MIA was more frequent in the sublobar-resected cohort than in the lobar-resected cohort (65% vs. 30%), whereas poorly differentiated tumors were less frequent (3.4% vs. 8.6%).

Table 1 Patient characteristics

Out of the 564 patients studied after surgery, 21 patients passed away (5 in the 0.7 ≤ CTR < 1 category and 16 in the CTR = 1 category), while 32 patients experienced recurrence (6 in the 0.7 ≤ CTR<1 category and 26 in the CTR = 1 category) over the observation period. The 5-year RFS and OS rates of all 564 patients were 94.3% and 96.3%, respectively. Figure 2 demonstrates that there were no disparities in mortality or recurrence rates between the sublobar resection and lobar resection groups over a 5-year period, with OS rates at 96% vs. 96.6% (P = 0.674) and RFS rates at 93.3% vs. 95.5% (P = 0.253). Table 2 shows the results of univariate and multivariate analyses for clinicopathological features associated with recurrence.

Fig. 2

Survival outcome between lobar resection and sublobar resection groups in small(≤ 2 cm) early-stage lung adenocarcinoma(A, RFS; B, OS). The 5-year RFS and OS were similar between the lobar resection and sublobar resection groups. RFS, recurrence-free survival; OS, overall survival

Table 2 Cox proportional hazard model for the 5-year recurrence-free survival in 564 patients

In the univariate analysis of RFS, male sex, age > 56 years, Maximum tumor size > 1 cm, consolidation component size > 1 cm, and CTR ≥ 0.75 were associated with a lower RFS. Regarding the correlation between the CTR and pathology grade (r = 0.739, P < 0.001), we excluded the pathology grade from the multivariate analysis. Moreover, since the surgical approach has some impact on the prognosis of lung adenocarcinoma ≤ 2 cm, we enrolled the surgical approach in the multivariate analysis. Multivariate analysis identified that CTR ≥ 0.75(HR = 82.952, 95%CI 8.732, 788.019), age > 56 years (HR = 3.850, 95%CI 1.442, 10.273), and sublobar resection(HR = 3.612, 95%CI 1.750, 7.453) could predict worse survival.

Survival outcomes according to CTR classification

In the context of multivariate analysis, we delved deeper into the influence of CTR on survival by categorizing the 564 patients into six subgroups based on different ranges of CTR values: 0 ≤ CTR<0.5, 0.5 ≤ CTR<0.6, 0.6 ≤ CTR<0.7, 0.7 ≤ CTR<0.75, 0.75 ≤ CTR<0.8, 0.8 ≤ CTR<1, and CTR = 1. Figure 3A illustrates the 5-year RFS based on CTR, with rates of 100% for 0 ≤ CTR<0.5, 100% for 0.5 ≤ CTR<0.6, 100% for 0.6 ≤ CTR<0.7, 94.4% for 0.7 ≤ CTR<0.75, 93.8% for 0.75 ≤ CTR<0.8, 90.9% for 0.8 ≤ CTR<1, and 77.8% for CTR = 1. The 5-year overall survival rates based on CTR were as follows: 100% (0 ≤ CTR<0.5), 100% (0.5 ≤ CTR<0.6), 100% (0.6 ≤ CTR<0.7), 94.4% (0.7 ≤ CTR<0.75), 100% (0.75 ≤ CTR<0.8), 90.9% (0.8 ≤ CTR<1), 86.3% (CTR = 1) (Fig. 3B). It is evident that there were no notable variances in RFS and OS between the ranges of 0 ≤ CTR<0.5, 0.5 ≤ CTR<0.6, and 0.6 ≤ CTR<0.7. Additionally, there were no notable variances in RFS and OS between the ranges of 0.7 to less than 0.75, 0.75 to less than 0.8, and 0.8 to less than 1 (P = 0.852 and P = 0.442, respectively). Consequently, the patients were categorized into three groups based on their CTR values: CTR < 0.7, 0.7 ≤ CTR<1, and CTR = 1. The three groups showed notable variations in the 5-year RFS and 5-year OS, as depicted in Fig. 3C and D. As shown in Table 3, there were 369 CTR < 0.7, 78 0.7 ≤ CTR<1, and 117 CTR = 1. Patients with CTR > 0.7 comprised more males (P < 0.001) and more patients aged > 56 years (P < 0.001). In addition, patients in the CTR>0.7 groups had a higher solid component size (P < 0.001), a greater number of patients with low differentiation degree (P < 0.001), a higher number of patients diagnosed with IAC (P < 0.001), and a lower number of patients who underwent sublobar resection (P < 0.001) compared to the CTR<0.7 group.

Fig. 3

Survival outcomes according to CTR. There were no significant differences in RFS and OS among 0 ≤ CTR<0.5, 0.5 ≤ CTR<0.6, and 0.6 ≤ CTR<0.7 and in RFS and OS among 0.7 ≤ CTR<0.75, 0.75 ≤ CTR<0.8, and 0.8 ≤ CTR<1(P = 0.852 and P = 0.442, respectively); Significant differences existed in 5-year RFS and 5-year OS among 0 ≤ CTR<0.7, 0.7 ≤ CTR<1, and CTR = 1. CTR, consolidation-to-tumor ratio; RFS, recurrence-free survival; OS, overall survival

Table 3 Clinicopathologic characteristics of 564 patients in CTR<0.7, 0.7≤CTR<1 and CTR=1 groupsComparison of survival rates in patients undergoing lobar resection versus sublobar resection with CTR values less than 0.7, between 0.7 and 1, and equal to 1

After analyzing the results using the CTR classification, we found significant differences in both the 5-year RFS and OS between the lobar resection and sublobar resection groups with a CTR between 0.7 and 1. Specifically, the 5-year RFS was 100% vs. 76.9% (P < 0.001) and the 5-year OS was 100% vs. 80.8% (P = 0.001) as shown in Fig. 4A and B. In the case of CTR = 1, the 5-year recurrence-free survival rate was 85.7% for those who underwent lobar resection and 57.6% for those who had sublobar resection (P = 0.001) (Fig. 4C); the 5-year overall survival rate was 89.3% for lobar resection and 78.8% for sublobar resection (P = 0.125) (Fig. 4D). The data suggests that patients who underwent lobar resection had better clinical results compared to those who had sublobar resection, for both CTR values of 0.7 ≤ CTR<1 and CTR = 1. Yet, patients with CTR values between 0 and 0.7 showed no variance in RFS and OS outcomes when comparing lobar resection to sublobar resection groups (5-year RFS, 100% vs. 100%; 5-year OS, 100% vs. 100%). The sublobar resection group was shown to be just as effective as the lobar resection group when it came to CTR < 0.7.

Fig. 4

Survival outcomes between lobar resection and sublobar resection groups in 0.7 ≤ CTR<1(A, RFS; B, OS), and CTR = 1(C, RFS; D, OS). Both the 5-year RFS and OS were significantly different between the lobar resection and sublobar resection groups in 0.7 ≤ CTR<1(P < 0.001 and P = 0.001, respectively); AS for CTR = 1, the survival outcome was significantly different between the lobar resection and sublobar resection groups in RFS(P = 0.001). CTR, consolidation-to-tumor ratio; RFS, recurrence-free survival; OS, overall survival

Survival outcomes among 0 ≤ CTR<0.7, 0.7 ≤ CTR<1and CTR = 1 in each surgery approach

The lobar resection groups showed similar RFS and OS between 0 ≤ CTR<0.7 and 0.7 ≤ CTR < 1, both at 100%, slightly higher than CTR = 1 (P = 0.005 and P = 0.016), as depicted in Fig. 5A and B. In the sublobar resection groups, however, 0 ≤ CTR<0.7 had a significantly higher RFS (Fig. 5C) and OS (Fig. 5D) compared with 0.7 ≤ CTR < 1 (P < 0.001 and P < 0.001). The 5-year RFS and OS of 0 ≤ CTR<0.7 with sublobar resection was equivalent to that of 0 ≤ CTR<0.7 with lobar resection.

Fig. 5

Survival outcomes among 0 ≤ CTR<0.7, 0.7 ≤ CTR<1 and CTR = 1 in lobar resection(A, RFS; B, OS) and sublobar resection(C, RFS; D, OS) and comparison of survival outcomes among them(E, RFS; F, OS). The 5-year OS of the lobar resection group was excellent, showing 89% or more regardless of CTR values. CTR, consolidation-to-tumor ratio; RFS, recurrence-free survival; OS, overall survival

A CTR between 0.7 and 1 after lobar resection showed similar 5-year RFS and OS rates compared to a CTR between 0 and 0.7 after sublobar resection (Figs. 5E and F and 100% vs. 100%). Nevertheless, a CTR of 1 following lobar resection resulted in notably reduced RFS and OS in comparison to a CTR between 0.7 and 1 following lobar resection (P = 0.005 and P = 0.016) (Fig. 5E and F). A CTR of 1 after lobar resection showed similar 5-year RFS and OS compared to a CTR of 0.7 to less than 1 after sublobar resection (P = 0.243 and P = 0.203, respectively) (Fig. 5E and F).