Prognostic Relevance of Mucinous Subtype in a Population-based Propensity Score Analysis of 40,083 Rectal Cancer Patients.

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The prognostic relevance of mucinous histology in colorectal cancer remains unclear, especially for rectal neoplasms. The objective of this study was to evaluate if mucinous subtype has a relevant impact on overall survival (OS) and cancer-specific survival (CSS) of patients with adenocarcinomas of the rectum. On the basis of the data set of the Surveillance, Epidemiology, and End Results Program of the National Cancer Institute of the United States, patients with rectal cancer between 2004 and 2011 were identified. Risk-adjusted Cox regression analysis and propensity score methods were used to assess OS and CSS. In total, 40,083 patients with stage I-IV rectal cancer, of whom 2483 (6.2%) had mucinous histology, were included in this study. In unadjusted analysis, the 5-year OS and CSS for patients with a mucinous adenocarcinoma was 54.3% [95% confidence interval (CI) 52.0-56.7] and 61.4% (95% CI 59.1-63.9) compared to 66.4% (95% CI 65.8-67.0) and 74.5% (95% CI 73.9-75.1) for patients with nonmucinous adenocarcinoma (P<0.001). The survival disadvantage persisting in risk-adjusted Cox proportional hazard regression analysis [hazard ratio (HR) 1.23, 95% CI 1.15-1.31, P<0.001 and 1.25, 95% CI 1.16-1.35, P<0.001) disappeared after propensity score matching (OS: HR=0.96, 95% CI 0.76-1.21, P=0.722; CSS: HR 1.06, 95% CI 0.80-1.40, P=0.693). This population-based, propensity score matched analysis shows that mucinous histology itself does not constrain survival in rectal cancer patients. Therefore, treatment decisions should not be different according to mucinous histology.