CDO1 and cancer: We have demonstrated that other types of cancer have also exhibited clinical and prognostic relevance of aberrant cancer-specific promoter DNA methylation of CDO1 gene, such as breast, esophageal, colorectal and gallbladder cancer.[8–10,12,16] Among such well-documented literatures, promoter DNA hypermethylation of CDO1 reproducibly represents more aggressive phenotypes independently of tumor stage in a multivariate prognostic analysis, and our current study also supported the hypothesis that CDO1 gene may have predictive value of prognosis in primary BTC.