The combination of metabolite markers, including d-glucose and d-mannose for colon cancer diagnosis and 2-aminobutanoic acid, 3-hydroxypyridine, d-glucose, d-mannose, isoleucine, l-tryptophan, urea, and uric acid for rectal cancer diagnosis, showed superior predictive performance compared to CEA and CA 19-9 [24]. This evidence concerns the gene CEACAM5 and rectal cancer.