CEA is a tumour marker, which means its presence in the blood may indicate the presence of cancer. It is mainly used to monitor the effects of treatment and the recurrence of certain cancers. High levels can be detected in patients with colorectal or other types of cancer including medullary thyroid, breast, colon, liver, lung, ovarian, pancreatic and prostate cancer. The concentration of CEA in the blood does not accurately reflect tumour size, but patients with more advanced tumours or metastases are likely to have higher levels. It is important not to interpret CEA levels as absolute evidence of the presence or absence of cancer. Levels of CEA are analyzed in light of a clinical assessment and other diagnostic tests. Also note that conditions such as liver disease or inflammatory bowel disease and certain lifestyles such as cigarette smoking can lead to an increase in CEA. Variations between laboratories can be seen with this test based on the different testing techniques they use. It is therefore recommended to always use the same laboratory for ongoing CEA monitoring.