According to the inclusion and exclusion criteria, a total of 373 patients were enrolled in our analysis, including 138 patients in the LRC group and 235 patients in the M/HRC group. After propensity score matching at a ratio of 1:1 based on the variables mentioned above, 99 LRC patients were matched with 99 M/HRC patients.
Characteristics and short-term outcome for the total cohort
The clinicopathologic characteristics of the patients are summarized in Table 1. In the total cohort, there were more elderly patients in the M/HRC group compared with the LRC group (P=0.027). The pathological T stage and TNM stage of tumors were more advanced in the M/HRC group than in the LRC group (P＜0.001 and P=0.002). Perineural invasion happened more often in the M/HRC group (P=0.009), while more patients received NAT in the LRC group (P＜0.001). There were no statistical differences in the aspect of other clinicopathologic factors between the two groups.
Operative results of the patients are shown in Table 2. Of all cases, more patients underwent non-restorative surgery in the LRC group (P＜0.001), and in patients receiving restorative surgery, more patients beared protective ostomy in the LRC group compared with the M/HRC group (P＜0.001). Meanwhile, the LRC group had longer operative time and more blood loss volume than the M/HRC group (P＜0.001). There were no significant differences between the two groups in terms of the distal resection margin, CRM status and conversion to open surgery, except for a smaller number of harvested lymph nodes in the LRC group (P＜0.001). The overall morbidity in LRC patients was 17.4%, which was higher than M/HRC patients (10.2%, P=0.046). However, there were no significant differences in reoperation rate and the length of postoperative hospital stay between the two groups. No mortality occurred in both groups.
Short-term outcome for the matched cohort
After propensity score matching, there were no longer any significant differences between the LRC group and M/HRC group for most of the baseline characteristics, especially for age, pathological TNM stage, perineural invasion and whether receiving NAT (Table 1). Similar to the total cohort, more patients received non-restorative surgery in the LRC group compared with the M/HRC group (P＜0.001). Of the 71 non-restorative procedures, 40 cases of APR, 24 cases of ELAPE and 3 cases of Hartmann's procedure were performed in the LRC group, while 2 cases of APR, 1 case of ELAPE and 1 case of Hartmann's procedure were performed in the M/HRC group. The LRC group demonstrated a statistically significant longer operative time (P＜0.001) and more blood loss volume (P=0.015) when compared with the M/HRC group. There were no significant differences between the two groups in terms of the distal resection margin, CRM status, number of harvested lymph nodes and conversion to open surgery, except for more frequent protective ostomy in the LRC group (P=0.001). The LRC patients were inclined to have more postoperative morbidity compared with M/HRC patients (16.2% vs. 8.1%, P=0.082), which may prolong the length of hospital stay for LRC patients to some extent (P=0.011). However, the reoperation rate and 30-day mortality were statistically insignificant between the two groups (Table 2).
Long-term outcome for the matched cohort
The median follow-up period was 63 months (range, 4-124 months) for the matched cohort. Recurrence was observed in 42 patients: 9 had local recurrence, 29 had distant metastasis and 4 developed local and distant recurrence synchronously. As a whole, recurrence was more frequent in the LRC group compared with the M/HRC group. Separately, the LRC patients tended to have a higher risk of distant metastasis than M/HRC patients (21.2% vs. 12.1%, P=0.086). However, the incidence of local recurrence was 9.1% in the LRC group and 4.0% in the M/HRC group, which was statistically insignificant (P=0.251). The patterns of recurrence are described in detail in table 2. On Kaplan-Meier analysis, the 5-year OS was 77.0% for LRC patients and 86.4% for M/HRC patients (P=0.033, Figure. 1); the 5-year DFS was 71.2% and 86.2%, respectively (P=0.017, Figure. 2).
Based on univariate analysis, age (p=0.001), tumor location (P=0.033), preoperative CEA level (P=0.043), preoperative CA19-9 level (P=0.006), pathological T stage (p=0.008), N stage (P＜0.001), lymphovascular invasion (P＜0.001) and postoperative complications (P=0.003) were revealed as significant predictors of OS (Table 3). On multivariate analysis, only age (HR=4.236, 95% CI 1.915-9.368, P＜0.001), pathological N stage (HR=5.006, 95% CI 1.874-13.368, P=0.001) and lymphovascular invasion (HR=3.086, 95% CI 1.368-6.960, P=0.007) remained as independent factors of OS (Table 4).
Considering the DFS, univariate analysis revealed age (P=0.010), ASA score (P=0.036), tumor location (P=0.017), preoperative CA19-9 level (P=0.019), pathological N stage (P=0.026), number of harvested lymph nodes (P=0.018), CRM status (P＜0.001) and neoadjuvant CRT (P=0.035) as significant predictors of DFS (Table 3). On multivariate analysis, only tumor location (HR=2.305, 95% CI 1.203-4.417, P=0.012), preoperative CA19-9 level (HR=2.362, 95% CI 1.014-5.505, P=0.046), pathological N stage (HR=2.438, 95% CI 1.239-4.797, P=0.010) and CRM status (HR=8.609, 95% CI 2.826-26.228, P＜0.001) were independent predictors of DFS (Table 4).