Potential impact of lateral lymph node dissection (LLND) for low rectal cancer on prognoses and local control: A comparison of 2 high-volume centers in Japan that employ different policies concerning LLND

Background. Controversy remains around whether the addition of lateral lymph node dissection to total mesorectal excision offers benefits in terms of survival or local control to patients with low rectal cancer. This study aimed to examine the impact of lateral lymph node dissection in the treatment of low rectal cancer on prognosis and local control and to identifi patients who might benefit from lateral lymph node dissection at 2 high-volume centers in, apan that employ different policies with regard to adopting lateral lymph node dissection. Methods. We reviewed outcomes from a total of 1,191 consecutive patients with low rectal cancer (rectal cancer distal to the peritoneal reflection) who underwent total mesorectal excision plus lateral lymph node dissection at 2 high-volume centers (the National Cancer Center and Aichi Cancer Center) in Japan. To assess the therapeutic outcomes of the respective node dissections, we applied an index calculated by multiplying the incidence by the 5 year overall survival of patients with metastasis in the respective lateral node stations. Multivariate analyses were performed to determine independent risk factors for local recurrence and prognostic factors. Results. Outcomes according to the presence or absence of lateral nodal metastases showed long-term survival with lateral dissection, even in patients with lateral nodal metastases (5-year overall survival: 53.1 % at the National Cancer Center vs 45.2% at Aichi Cancer Center), while stage I to III patients with no lateral nodal metastases had very good prognoses at both centers (5-year overall survival: 81.7% at the National Cancer Center vs 81.0% at Aichi Cancer Center). According to the index of estimated benefit from lateral lymph node dissection, dissection of the distal internal iliac nodes and obturator nodes yielded the greatest therapeutic benefit in patients at both centers. Compared to patients with bilateral lateral lymph node dissection, the relative risk for local recurrence was 2.0 for those with unilateral lateral lymph node dissection. Conclusion. Lateral lymph node dissection outcomes observed at the 2 high-volume centers in Japan demonstrate high reproducibility with good results in terms of prognosis. Differences in policies concerning the adoption of lateral lymph node dissection affected local recurrence rate.