Tumor markers are the substances found in the serum that indicate the presence of the tumor. The most common tumor markers are alpha-fetoprotein (AFP), beta-human chorionic gonadotropin (beta-hCG), BRC1 and BRCA2, and carcinoembryonic antigen (CEA).
CEA, the carcinoembryonic antigen, was described in 1965 by Phil Gold and Samuel O. Freedman. The scientists identified the substance in extracts of human colon extracts.
It is a glycoprotein normally produced during the embryonal development and in low concentrations by the colon in adults.
CEA is a group of glycoproteins, which contain 45-55% carbohydrate and have a molucelar mass of 150-300 kDa (the mean molecular mass is 180 kDa). The antigen consists of 641 aminoacids that form a single chain. CEA proteins are regulated by the genes located on the chromosome 19 (CEACAM1, CEACAM3-8, CEACAM16, CEACAM18-21).
The family of CEA includes approximately 36 different proteins.
- ≤3 ng/L – is considered to be a normal level of CEA for non-smokers;
- ≤5 ng/L – is considered to be a normal level of CEA for smokers;
- ≤ 10 ng/L – a moderate increased CEA typical for smokers;
|Cancers||Non-cancerous (benign conditions)|
Clinical use for colorectal cancer
The measurement of CEA in colorectal cancer provides the following information:
- To identify the cancer – The concentration of CEA increased in 5-10 times from the upper reference limit suggests the colon cancer, although other cancers may also be present;
- The stage of cancer – it is considered that in colorectal cancer the concentrations of CEA correlate with the stage of the disease;
- The metastases – High CEA levels seen before the treatment determine the possibility of metastases;
- The monitoring of the cancer after the initial treatment – It is known that after the initial treatment the concentration of CEA in the serum decreases within several weeks after the surgery and remains stable during the remission. When the tumor recurs the concentration of the CEA rises, the levels of CEA antedates the clinical recurrence of the disease for approximately 5 months. This measurement as a recurrence predictor is supposed to be accurate in 90% of cases. It is recommended to measure the CEA concentration at the beginning of treatment and then every 1-3 months during active treatment. Sometimes the levels of CEA may rise spontaneously when the new therapy is started, especially when oxaliplatin is administered;
Clinical use for other types of cancer
In other types of cancers CEA concentrations are used:
- CEA is less sensitive in breast cancer than CA15-3 or CA27-29. In early or localized breast cancer the CEA concentrations may remain normal;
- The CEA concentrations are helpful to monitor the breast cancer during the treatment and the development of the metastases, to predict the response to chemotherapy and the surveillance;
- CEA is useful to make a diagnosis of non-small cell lung carcinoma and monitor the cancer. It was estimated that CEA concentrations are increased in more than 65% of cases;
- Recombinant monoclonal antibody to CEA Arcitumomab (anti-carcinoembryonic antigen) marked with radioisotope is used to detect the malignancies, especially breast and colorectal cancers, as it binds to CEA producing cells.