CEACAM5 and breast cancer: In addition to CEA and CA15-3, CYFRA 21-1 (derived from the words cytokeratin fragment 21.1), the most sensitive tumor marker used in monitoring non-small cell lung cancer [28]-[29], has been reported to be detected in the peripheral blood from patients with metastatic breast cancer and proposed to be used in monitoring disease relapse and treatment response in breast cancer patients [23]–[24], [30].