Markers included CA 125 for ovarian cancer, Cyfra21-1 for lung cancer, CA15-3 for breast cancer, CA19-9 for pancreatic cancer, carcinoembryonic antigen (CEA) for colorectal, pancreatic, breast, and lung cancer, and alpha-fetoprotein (AFP) for liver cancer [34,35,36]. Here, AFP is linked to lung cancer.