Even the simultaneous use of serum markers CA15-3 and carcinoembryonic antigen (CEA) results in diagnosing metastasis in up to 60–80% of patients with breast cancer early [13–17], while according to our unpublished data, the simultaneous use of both CA15-3 and CEA resulted in the early diagnosis of metastasis in less than 50% of patients with breast cancer. Here, CEACAM5 is linked to breast cancer.