Correlations between the Recurrence Patterns and Sizes of Lateral Pelvic Lymph Nodes before and after Chemoradiotherapy in Patients with Lower Rectal Cancer

Objective: Factors that predict rectal cancer metastasis to the lungs remain undefined. We investigated whether the lateral pelvic lymph node (LPN) sizes before and after chemoradiotherapy (CRT) correlate with lung metastasis after surgery for lower rectal cancer. Methods: Two hundred and forty patients with lower rectal cancer who received preoperative CRT and curative surgery between 2003 and 2017 were examined. Computed tomography-measured LPN sizes before and after CRT were retrospectively determined by 1 colorectal surgeon who was blinded to the patients’ clinical and pathological outcomes. Results: The 5-year cumulative lung metastasis rates were 15.2%. The mean LPN sizes in patients who developed lung metastasis were larger than those in patients who did not (pre-CRT: 8.7 vs. 6.3 mm, p = 0.003; post-CRT: 6.8 vs. 4.5 mm, p = 0.001). The cumulative lung metastasis rate in patients with large LPNs was higher than in those with small LPNs both before and after CRT. On multivariate analysis, lung metastasis was independently correlated with the LPN size only after CRT (hazard ratio [HR]: 5.58), together with the ypT stage (HR: 2.96) and the tumor location (HR: 0.38). Conclusions: LPN size after CRT is strongly predictive of postoperative lung metastasis in patients with lower rectal cancer.