CEACAM5 and breast cancer: At present, American National Cancer Institute lists the protein tumour markers that are now used in clinic, for example, alpha‐fetoprotein (AFP) for liver cancer and germ cell tumours, CA15‐3 for breast cancer, CA19‐9 for pancreatic cancer and gastric cancer, CA‐125 for ovarian cancer, carcinoembryonic antigen (CEA) for colorectal cancer and some other cancers, and so on.