CEACAM5 and cancer: Cancer antigen 15-3 (CA15-3), cancer antigen 27-29 (CA27-29), and carcinoembryonic antigen (CEA), which are the only blood tumor markers for breast cancer, are not recommended by the European Group on Tumor Markers (EGTM) and the American Society of Clinical Oncology (ASCO) guidelines for such purposes due to their lack of sensitivity and the insufficient evidence of their roles in early-stage breast cancer management [8,9].