Tumor markers are the substances found in the serum that indicate the presence of the tumor.
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 an adult.
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 (about 10 genes). The half life of CEA is from 3 to 13 days.
The family of CEA includes approximately 36 different proteins.
- < or = 3 ng/L – is considered to be a normal level of CEA for non-smokers;
- <or = 5 ng/L – • is considered to be a normal level of CEA for smokers;
- < 10 ng/L – a moderate increased CEA typical for smokers;
See also: Sarcomatoid carcinoma
The indications for the CEA test include the following:
- To assess the stage of cancer;
- To monitor the results of the cancer treatment and recurrence of the tumor;
- To identify the metastases and dissemination of the cancer the test is performed not only with the serum, but with the cerebrospinal fluid, fluids from the pleural or peritoneal cavity;
- In combination with other tumor markers may be used to evaluate the cancer;
- However, as long as CEA may be elevated not only in cancer, but also in other many non-cancerous conditions, it cannot be used as the only method to determine the cancer.
A blood sample is taken from the vein by the means of venepunction. It takes about 3 days before the result is available.
Measurement methods include:
- RIA (Radioimmunoassay);
- IRMA (Immunoradiometric assay);