DPYD and rectal cancer: Measurement of serum CEA levels is inexpensive, standardized for normal limit, widely used and easily performed, as compared with other potential prognostic markers for rectal cancer patients, such as CA 19–9, p53, ras expression, thymidine synthase, dihydropyrimidine dehydrogenase, 18q loss of heterozygosity, deleted in colon cancer (DCC) protein, DNA ploidy or micro-RNA signature [11,17,18].