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, 130 LRC patients were matched with 130 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 and perineural invasion (Table 1). Similar to the total cohort, more patients received NAT and non-restorative surgery in the LRC group compared with the M/HRC group (P<0.001). Of the 95 non-restorative procedures, 48 cases of APR, 40 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<0.001) 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 and conversion to open surgery as well, except for a smaller number of harvested lymph nodes in the LRC group (P<0.001). The LRC patients were inclined to have more postoperative morbidity compared with M/HRC patients (18.5% vs. 10.0%, P=0.051). Despite this, reoperation rate, the length of postoperative hospital stay 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 62 months (range, 8-118 months) for the matched cohort. Recurrences were observed in 48 patients: 11 had local recurrence, while 37 had distant metastasis. The incidence of local recurrence was 6.2% in the LRC group and 2.3% in the M/HRC group, which was statistically insignificant (P=0.216). However, distant metastasis rate was higher for LRC patients than M/HRC patients (19.2% vs. 9.2%, P=0.021). The patterns of recurrence are described in detail in table 2. On Kaplan-Meier analysis, the 5-year OS was 78.1% for LRC patients and 88.8% for M/HRC patients (P=0.008, Fig. 1); the 5-year DFS was 76.2% and 89.0%, respectively (P=0.004, Fig. 2).
Based on univariate analysis, BMI (p=0.008), tumor location (P=0.008), preoperative CEA level (P=0.013), preoperative CA19-9 level (P=0.001), pathological T stage (p=0.001), N stage (P<0.001), TNM stage (P<0.001), lymphovascular invasion (P<0.001) and postoperative complications (P=0.020) were revealed as significant predictors of OS (Table 3). On multivariate analysis, only BMI (HR=1.908, 95% CI 1.028-3.541, P=0.041), tumor location (HR=2.095, 95% CI 1.142-3.843, P=0.017), pathological N stage (HR=5.775, 95% CI 2.875-11.600, P<0.001) and postoperative complications (HR=2.024, 95% CI 1.054-3.886, P=0.034) remained as independent factors of OS (Table 4).
Considering the DFS, univariate analysis revealed tumor location (P=0.004), preoperative CEA level (P=0.035), preoperative CA19-9 level (P<0.001), pathological N stage (P=0.001), TNM stage (P=0.003), type of operation (P=0.021) and number of harvested lymph nodes (P=0.016) as significant predictors of DFS (Table 3). On multivariate analysis, only tumor location (HR=2.320, 95% CI 1.251-4.303, P=0.008), preoperative CA19-9 level (HR=3.376, 95% CI 1.620-7.037, P=0.001), pathological N stage (HR=3.351, 95% CI 1.777-6.318, P<0.001) and number of harvested lymph nodes (HR=2.981, 95% CI 1.601-5.552, P=0.001) were independent predictors of DFS (Table 4).