Lymph node status and its impact on the prognosis of left-sided and right-sided colon cancer: A SEER population-based study.

Background: Some significant differences exist between the outcomes of left- and right-sided colon cancer patients. The presence of nodal metastases is a critical prognostic factor, especially in the absence of distant metastasis. Our research studied the lymph nodes status of left- and right-sided colon cancer patients to determine the influence of this factor on prognosis.

Methods: Our data were obtained from the Surveillance, Epidemiology and End Results (SEER) database. We used the chi-square test to analyze the clinicopathological characteristics. The X-tile program was adopted to acquire optimal cutoff points of lymph node index. Kaplan-Meier curves were used to analyze prognosis and multivariate Cox regression models were performed to identify the independent factors associated with survival. Nomograms were built to predict the overall survival of patients, Harrell's C-index and calibration plots were used to validate the nomograms.

Results: The study included 189,941 patients with colon cancer without metastasis (left 69,885, right 120,056) between 2004 and 2015. There are more patients with adequate examined lymph nodes in right-sided. Lymph node status in patients with right colon cancer has a more significant impact on the risk of death. LODDS (C-index: 0.583; AIC: 6875.4) was used to assess lymph node status. The nomograms showed that lymph node status was the main factor to predict the outcome in right-sided colon patients.

Conclusions: The influence of lymph node status on predicting prognosis is significantly different between patients with left and right colon cancer without metastasis. The tumor site needs to be considered when lymph node status is used to assess the outcome of patients.