CEACAM5 and breast neoplasm: Carcinoembryonic antigen (CEA), with a normal concentration lower than 5 ng/mL in serum of healthy humans [4,5] and increased concentration induced by various cancers, is one of the most important clinical cancer biomarkers for the diagnosis of colon tumors, breast tumors, ovarian carcinoma, colorectal cancer, and cystadenocarcinoma [6,7,8,9].