Baseline MRI detected lateral lymph node as a prognostic factor: a cohort study in pN0 low-risk rectal cancer

It is highly controversial that how to deal with the lateral lymph-node metastasis in patients with rectal cancer. Although lateral lymph node can be detected by preoperative MRI, the metastasis status cannot be accurately determined following standard total mesorectal excision (TME) in low-risk patients. This study was to assess the correlation between preoperative MRI detected lateral lymph-node (LLN) features and prognosis in patients with non-preradiated low recurrence risk rectal cancers.

This retrospective study included 593 low-risk rectal cancers underwent TME without neoadjuvant chemo-radiotherapy from January 2013 to December 2015. The features of the largest LLN were retrospectively reviewed on preoperative MRI. The relationship of MR-LLN features with overall survival, metastasis-free survival, and local relapse-free survival was analyzed.

A total of 593 patients including 415 cases of pN0, 86 cases of pN1, and 92 cases of pN2 were enrolled in this study. In pN0 patients, at least one visible LLN was detected in 104 patients on primary MRI. The MR-T staging, postoperative therapy status, the presence of MR-LLN, and short axis (SA) of MR-LLN were significantly correlated with the recurrence in pN0 patients (all p < 0.05). The OS and MFS were significantly lower in patients with MR-LLN SA ≥ 8 mm than SA < 8 mm (p < 0.01, HR = 4.35, 95% CI = 1.48-12.77). The OS and MFS of patients with pN0-LLN(+) and SA ≥ 8 mm were similar to pN2-LLN(-) patients. The location of MR-LLN showed no significant impact on prognosis.

For low-risk rectal cancers without neoadjuvant chemo-radiotherapy, the presence of MR-LLN is associated with poor prognosis. The pN0-LLN(+) SA ≥ 8 mm patients might be concerned as pN2 patients and receive more intensive neoadjuvant or adjuvant treatment.