Blood samples can be easily obtained, but serum BC‐specific biomarkers, such as cancer antigen 15‐3 (CA 15‐3) and carcinoembryonic antigen (CEA), have low sensitivity and specificity, and thus are not useful in the early detection of BC.7 American Society of Clinical Oncology recommends the use of CEA and CA 15‐3 only in metastatic BC (MBC).8 To improve the survival of BC patients, it is necessary to find a reliable biomarker allowing better cancer screening and early diagnosis. Here, CEACAM5 is linked to cancer.