Intervention: In patients with proven colon cancer, five extra biopsies will be taken from the tumour during endoscopy to determine CpG methylation of Wnt target genes in fresh tumor samples. Next, these patients will pre-operatively receive decitabine as a single intravenous infusion at a dose of 45 mg/m2 over 6 hr. After resection, Wnt target gene expression and CpG methylation of Wnt target genes will again be determined in fresh tumor samples.