Abstract: A blood-based biomarker for cancer includes a specific amino acid group of at least seven amino acids. The at least seven amino acids include histidine, isoleucine, leucine, methionine, tryptophan, valine, and tyrosine. The specific amino acid group may further include phenylalanine. The cancer is at least one kind of cancer selected from the group consisting of liver cancer, colon cancer, lung cancer, gall bladder cancer, lymph node metastatic cancer, gastric cancer, pancreas cancer, bile duct cancer, breast cancer, malignant mesothelioma, and T-cell leukemia/lymphoma.