Use of lymph node ratio to guide clinical decision-making concerning adjuvant radiotherapy in pT1-2N1 rectal cancer.

ABSTRACT

PURPOSE: Lymph node metastases are uncommon in pT1-2 rectal cancer. pT1-2N1 are often characterized with low tumor burden and intermediate prognosis. Therefore, adjuvant radiotherapy (ART) is controversial in these patients. This study aimed to investigate the value of ART in pT1-2 rectal cancer and evaluate the guiding role of lymph node ratio (LNR) for utilization of ART. METHODS: pT1-2N1 rectal cancer patients who received surgery without neoadjuvant radiotherapy between 2000 and 2018 with at least 12 lymph node harvest were extracted from the Surveillance, Epidemiology and End Results (SEER) database. We used time-dependent receiver operating characteristic (ROC) analysis to determine the optimal cutoff of LNR. Kaplan-Meier methods and Cox proportional hazards regression models were performed to determine the prognostic value of ART in pT1-2N1 rectal cancer patients and subgroups stratified by LNR. RESULTS: A total of 674 and 1321 patients with pT1N1 and pT2N1 rectal cancer were eligible for analysis. There was no statistical cancer-specific survival (CSS) difference in pT1N1 rectal cancer patients between receiving and not receiving ART (P = 0.464). The 5-year CSS was 89.6% and 83.2% in pT2N1 rectal cancer patients between receiving and not receiving ART, respectively (P = 0.003). A total of 7.0% was identified as the optimal cutoff value of LNR. Survival improvement offered by ART was only found in LNR ≥ 7.0% subgroup (5-year CSS 89.5% versus 79.6%, P = 0.003) instead of LNR < 7.0% subgroup (5-year CSS 89.9% versus 86.3%, P = 0.208). CONCLUSION: ART show substantial survival benefit in pT2N1 rectal cancer patients with LNR ≥ 7.0%, warranting the conventional adoption of ART in this subgroup.