CEACAM5 and breast cancer: Serum tumour markers in BC include cancer antigen 15–3 (CA 15–3), carcinoembryonic antigen (CEA), cancer antigen 27–29 (CA27-29) and cancer antigen 125 (CA 125) (Tarighati et al. 2023; Moar et al. 2023; Seale and Tkaczuk 2022).