[Proximal pericolic lymph node metastasis beyond 10 cm in rectal cancer: patterns of prognostic impact of extended resection in a prospective cohort study]

Objective: To determine the actual metastasis rate of paracolic lymph nodes (PCN) more than 10 cm proximal to rectal tumors and explore the significance of PCN dissection in the prognosis of patients with rectal cancer. ​ Methods: This was a prospective observational cohort study. The clinical data of 457 consecutive patients with rectal cancer who underwent radical surgery at the Colorectal Tumor Center of West China Hospital, Sichuan University from January 2015 to May 2022 were included. Inclusion criteria: (1) Pathologically confirmed rectal adenocarcinoma (anal margin ≤ 12 cm); (2) R0 resection was performed with a proximal margin ≥ 10 cm (measured on the in vivo specimen during surgery after intestinal mobilization); (3) For stage IV patients, only those with resectable metastatic lesions by R0 were included; (4) Patients who completed the full course of neoadjuvant therapy (TNT) must meet the surgical window of 8-12 weeks after radiotherapy. Exclusion criteria: tumors located more than 15 cm from the anal margin, synchronous multiple primary colorectal cancers, positive tumor margins, preoperative imaging suggesting lateral lymph node metastasis (LLNM), presence of Lynch syndrome or familial adenomatous polyposis, emergency surgery, recurrence after rectal cancer surgery, T4b tumors requiring combined organ resection, previous radiotherapy and chemotherapy for non-rectal cancer, and those with cardiac, pulmonary, renal and other organ dysfunction that could not tolerate surgery. After standard total mesorectal excision (TME), the proximal intestinal tube was transected at a level more than 10 cm above the lesion, and then intestinal anastomosis or enterostomy was completed. The distance from the tumor edge was marked and measured in vivo during the operation, and lymph nodes were harvested from the fresh specimen. Patients with PCN metastasis beyond 10 cm proximal to the tumor were classified into the positive lymph node group (pPCN group), while those without PCN metastasis beyond 10 cm proximal to the tumor were classified into the negative lymph node group (nPCN group). The differences in clinicopathological characteristics, overall survival (OS) and disease-free survival (DFS) between the two groups were compared, and risk factor analysis and survival analysis of pPCN were performed. Results: There were 16 cases (3.5%) in the pPCN group, 15 cases (3.3%) had central lymph node metastasis; the nPCN group included 441 cases. When comparing the baseline characteristics between the pPCN group and the nPCN group, there was no statistically significant difference in other aspects except that the cN stage was more advanced in the pPCN group (P=0.006) (all P>0.05). The number of positive mesenteric lymph nodes in the pPCN group was higher than that in the nPCN group (P<0.001), and the proportion of patients with a total number of harvested lymph nodes ≥12 and the number of lymph nodes with a short diameter >5 mm were both higher (all P<0.05). The proportion of patients with positive lymph nodes within 10 cm and the number of positive lymph nodes within 10 cm were also higher in the pPCN group (both P<0.001). Similar to the clinical TNM staging, the proportions of patients with pT3 and N2 stages, as well as the incidence of poorly differentiated tumors (G3, G4) were higher in the pPCN group (P<0.001). The results of multivariate analysis showed that among the preoperative pathological characteristic variables, the presence of positive lymph nodes within 10 cm (OR=14.869, 95%CI: 2.993-73.858, P=0.001) and low tumor differentiation grade (OR=7.189, 95%CI: 2.091- 24.714, P=0.002) were independent risk factors for pPCN. The median follow-up time of the patients in this group was 63 (0-63) months. No local recurrence occurred in the pPCN group, and the 5-year OS was 50.0%, which was significantly lower than 78.0% in the nPCN group (HR=2.496, 95%CI: 1.263-4.930, P=0.008). The 3-year DFS was 43.8%, also significantly lower than 77.7% in the nPCN group (HR=2.950, 95%CI:1.488-5.846, P=0.002). Multivariate Cox prognostic analysis suggested that age ≥65 years (HR=2.041, 95%CI: 1.375-3.031, P<0.001), female (HR=1.838, 95%CI: 1.171-2.884, P=0.008), tumor length ≥3 cm (HR=1.747, 95%CI: 1.076-2.834, P=0.024), more advanced cT stage (HR=2.865, 95%CI: 1.234-6.653, P=0.014), and cM1 (HR=4.368, 95%CI: 2.480-7.694, P<0.001) were independent risk factors affecting OS. No neoadjuvant therapy (HR=0.636, 95%CI: 0.413-0.980, P=0.040) and cM1 (HR=5.556, 95%CI: 3.335-9.256, P<0.001) were independent risk factors affecting DFS. pPCN showed a tendency to be an independent risk factor for DFS (HR=1.942, 95%CI: 0.966-3.906, P=0.063). Conclusion: The incidence of pPCN is higher than expected, and the prognosis of patients is poor. Patients with high-risk factors may benefit from extended proximal intestinal resection (>10 cm) to avoid residual positive PCN, thereby reducing local recurrence.