Optimal number of lymph nodes for long-term survival in lymph node-negative rectal cancer: a population-based study.

PURPOSE: This study aimed to investigate the examined lymph node (ELN) count following lymph node-negative rectal cancer (RC) resection and to evaluate its influence on tumor stage migration and long-term survival among N0 patients. METHODS: A total of 5197 patients with N0/N1a RC were identified from the SEER database, comprising 1103 stage N0 patients and 208 stage N1a patients. Additionally, 462 RC patients from our center were analyzed, including 352 stage N0 and 110 stage N1a cases. Propensity score matching and multivariate Cox regression analyses were employed to reduce selection bias and adjust for potential confounders. RESULTS: The ELN threshold was determined to be 15 in both the SEER and QDUH cohorts (nonlinear P < 0.05). Patients in the adequate ELN group demonstrated better prognoses than those in the limited ELN group across both N0 and N1a stages. Comparable prognoses were observed between the N0-limited and N1a-adequate groups. Additionally, no statistically significant prognostic differences were identified between the ypN0 and pN0 groups. CONCLUSION: We propose that the 15 examined ELNs represent the optimal threshold for evaluating the quality of postoperative pathologic assessment and prognostic stratification in lymph node-negative RC patients. Additionally, patients with pN0 and ypN0 rectal cancers exhibit comparable oncologic outcomes, indicating that ypN0 nodal status after neoadjuvant radiotherapy for RC is not associated with adverse prognosis as compared with pN0 after primary surgery.