Prognostic Effect of Tumor Sidedness in Colorectal Cancer: A SEER-Based Analysis.

Background: The prognostic value of tumor sidedness in metastatic colorectal cancer (CRC) has been established, but its impact on nonmetastatic disease remains unclear. Our study aimed to explore the prognostic effect of tumor sidedness by subgroup survival analyses, according to histology and tumor grade in stage I-IV CRCs.
Methods: A retrospective population-based study was conducted based on Surveillance, Epidemiology and End Results (SEER) data. Population data in the SEER 9 registry (1975-2014) were used to determine survival trends of CRCs, and associated population data in the SEER 18 registry (2000 to 2014) were used to assess the prognostic impact of tumor sidedness on CRCs.
Results: The 5-year cause-specific survival for all subgroups of CRCs improved from 1975 to 2014. Of 238,826 patients, 44.2% had right-sided cancer. Patients with right-sided cancer were more likely to be older, to be women, to have disease of mucinous or signet-ring cell histology, to have more poorly differentiated tumors, and to be diagnosed with a more advanced disease stage. Multivariate Cox regression showed stage I-II right-sided cancers had better cause-specific survival than the left-sided cancers (left colon: hazard ratio [HR] = 1.091, 95% confidence interval [CI], 1.052-1.132; rectum: HR = 1.363; 95% CI, 1.304-1.425; P < .001), while stage III and IV right-sided cancers had worse cause-specific survival. In subgroup analyses by histology and tumor grade within stage III CRCs, right-sided poorly differentiated mucinous adenocarcinoma showed significantly better survival (left colon: HR = 1.352; 95% CI, 1.145-1.596; rectum: HR = 1.125; 95% CI, 0.916-1.381; P = .002).
Conclusion: The relationship between sidedness and prognosis in CRCs depends on stage and histopathologic characteristics, especially for stage III disease.
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