CEACAM5 and colorectal neoplasm: Carcinoembryonic antigen (CEA) is the most routinely used colorectal tumour marker, and is recommended by the National Academy of Clinical Biochemistry and American Society of Clinical Oncology for prognosis, monitoring response to treatment and for detecting metastatic disease and disease recurrence (Locker et al, 2006; Duffy et al, 2014).