Metastatic lymph node ratio as a prognostic factor after laparoscopic total mesorectal excision for extraperitoneal rectal cancer

The lymph node ratio (LNR; number of positive nodes divided by total nodes harvested) has been demonstrated to be a prognostic factor in colon cancer, but its role in extraperitoneal rectal cancer is still debated; furthermore, no data are available on laparoscopic rectal resection. The aim of this study was to evaluate the prognostic impact of LNR on long-term outcomes after laparoscopic total mesorectal excision (LTME) for extraperitoneal cancer in consecutive patients with a 5-year minimum follow-up. Methods This study is a prospective analysis of consecutive patients who underwent LTME for adenocarcinoma of the extraperitoneal rectum. Results LTME was performed in 158 patients. The median number of LN harvested was 12 (range = 3–25). The proportion of specimens with fewer than 12 examined LN was significantly higher in patients who had neoadjuvant chemoradiotherapy (p\0.001). During a median follow-up period of 122 months, the local recurrence rate was 8 %. At univariate analysis, disease-free survival and overall survival significantly decreased with increasing LNR (p\0.001). Multivariate analysis showed that the distal margin B1 cm was the only independent predictor of local recurrence (p = 0.028). LNR (cutoff value = 0.25) and lymphovascular invasion were significant prognostic factors for both disease-free (p = 0.015 and p = 0.046, respectively) and overall survival (p = 0.031 and p = 0.040, respectively). Even in the subgroup of patients in whom fewer than 12 LN were examined, LNR confirmed its prognostic role, with a statistical trend toward worse disease-free survival and overall survival. Conclusion Metastatic LNR is an independent prognostic factor for disease-free survival and overall survival after LTME for extraperitoneal rectal cancer.