Lateral Lymph Node Features and Tumor Regression Grade After Neoadjuvant Chemoradiotherapy for Locally Advanced Rectal Cancer: Impact on Oncological Outcomes.

The combination of neoadjuvant chemoradiotherapy (CRT) and total mesorectal excision (TME) is considered the standard treatment for locally advanced rectal cancer in the western world. Appropriate preoperative treatment and margin free surgery are key-elements in reducing the local-recurrence of the tumor and consequently improving overall survival.

Nevertheless, the local recurrence of stage II and III rectal cancer is still high, with current levels of 5% to 10% even when R0 resection is achieved. Most of the cases of loco-regional recurrence are associated with lateral lymph nodes (LLN) spread of cancer cells, which is not always controlled by the preoperative chemotherapy. As a matter of fact, the incidence of LLD metastases has been estimated to range from 11% to 22% in patients with T3/4 rectal cancer below the peritoneal reflection.

In order to improve these poor outcomes, Japanese surgeons have adopted extended lymphadenectomy with the dissection of lateral extramesorectal lymph nodes as the standard of care for T2-3 low rectal cancer patients5. While this approach is widely used in Japan and Korea, western surgeons have preferred a less aggressive approach, indicating lateral lymph node dissection (LLND) only in presence of clinically highly suspicious lateral pelvic lymph nodes on baseline magnetic resonance imaging (MRI). Thus, it is essential to identify preoperative predictive factors of LLN metastasis.

Even if MRI is considered the optimal diagnostic tool in rectal cancer, its accuracy for LLN staging is considered poor, especially after neoadjuvant treatment. LLNs often change in both features and size after CRT, and this behaviour might not be in concordance with the response of the primary tumor.

To the best of our knowledge, no consensus exists on whether the risk of local recurrence should be determined by assessing the features of LLN on the primary MRI or on the restaging MRI. Moreover, the relation between LLN response and primary tumor regression grade after neoadjuvant CRT needs to be thoroughly explored.

This multicenter cohort study aimed to investigate factors on primary and restaging MRI associated with lateral nodal recurrence and to identify patients who may benefit from LLND after neoadjuvant treatment for locally advanced rectal cancer.