CEA Test For Cancer - Carcinoembryonic Antigen Overview

Oncology, a field of medical science, involves diagnosis and treatment of cancer. Cancer, which is caused due to uncontrolled cellular division, is one of the biggest healthcare threats in developed as well as developing nations, with genetics and lifestyle equally fueling the 'killer' condition. The causative factors for this condition are many and early and timely diagnosis is the only path for successful treatment and remission.

Cancer diagnosis has grown to emerge as a separate field in medicine, with extensive research gifting abundant technological advancements. The most popularly used diagnostic modalities for cancer include pathological examination, biochemical studies and radiodiagnosis. Each diagnostic test recommended in cancer diagnosis has its own advantage and sensitivity, with biochemical analysis being done in almost all the affected cases.

What exactly are tumour markers?
Tumour markers are biochemical substances which can be detected in serum in the presence of a specific type of cancer. These can be considered as a trail left by cancerous cells or can be produced in response to them. Hence, their detection becomes a positive indicator: Two types of tumour markers have been identified:
1. Tumour markers produced by the body inresponse to cancer cells
alpha-fetoprotein (AFP), Beta-2-microglobulin (B2M), Beta-Human Chorionic Gonadotropin Hormone (Beta hCG), Bladder tumour antigen (BTA), CA 15-3, CA 19-9, Carcinoembryonic Antigen (CEA),etc
2. Tumour markers expressed by the cancer cells
Anaplastic lymphoma kinase (ALK), Epidermal growth factor receptor (EGFR), BRAF, Human epidermal growth factor receptor 2 (HER2), etc.

The discovery of tumour marker
The first tumour marker to be identified was the Beta hCG. The levels of this hormone are generally measured to determine pregnancy. However, high levels of this hormone have been linked to placental cancer or gestational trophoblastic disease. Later, in the year 1965, Phil Gold and Samuel 0. Freedman discovered CEA in a patient affected with colon cancer: Further research in this field, led to the detection of multiple tumour markers.

CEA as a cancer marker
CEA, initially postulated to be expressed normally in fetus and in adults only during cancer, was later identified to be present in low concentrations even in adults. CEA was first identified in developing fetus, especially in the first two trimesters, but the levels lowered in the third trimester: CEA produced in the colon is released into the gut lumen by apical columnar cells lining it. In case of colon cancer, this release mechanism is affected, resulting in increased concentration of the same in the blood. Thus, CEA came to be known as a stable tumour marker for colon cancer.

Structure of CEA
CEA is a glycoprotein with an approximate molecular weight of 200 KDa. The protein part consists of a single polypeptide chain belonging to the family of immunoglobulins. The N-terminal domain consists of 108 amino acids which is homologous to the variable region of the immunoglobulin molecule. The C-terminal domain of CEA usually consists of 26 amino acids.

The study on CEA continued for many years world over, post its structure being deciphered. Many analogous moieties of CEA were found to be cross-reactive antigens and the first CEA-related antigen discovered was Biliary Glyco Protein (BGP), followed by Nonspecific Cross-reacting Antigen (NCA) and CEA Gene Family Member (CGM) produced by the white blood cells. Apart from these, the most surprising was identification of Pregnancy Specific B1 Glycoprotein (PSG), a glycoprotein produced by placental syncytiotrophoblasts and secreted in maternal circulation.Presence of these cross-reacting antigens interfere with initial stage diagnosis of colorectal cancer. However, technology of hybridoma was developed to differentiate these close resembling biomolecules.

Only in colorectal cancer diagnosis? Though CEA levels have been linked to colorectal cancer, its high levels have also been linked to cancer of the pancreas, breast cancer, lung cancer, thyroid, etc. Apart from these, elevated CEA levels are also observed in gastrointestinal diseases like ulcerative colitis, diverticulitis, pancreatitis, etc. along with in cases of pulmonary infections and peptic ulcers. Thus, CEA can be considered as a broad spectrum biomarker with multiple diagnostic capability.

Steady rise in CEA post cancer treatment may be the first sign of CANCER recurrence.

Factors which increase serum levels of CEA
Normal serum levels of CEA is anywhere between 0 to 2.5 ng/mL. The levels differ between smokers and nonsmokers, with the values for the former being < 5.5 ng/mL, while in the later being <3.8 ng/mL. But, in few cases, the value is found to be increased even though the individual may not be affected by cancer or is a smoker. Few other conditions which may contribute to high CEA levels are:
- Inflammatory Bowel Diseases
- Lung infections
- Inflammation of the pancreas
- Stomach ulcers liver problems (like liver cirrhosis)
- Inflammation
- Gallbladder inflammation

CEA as a Tumour marker is used in
- Determining the prognosis of cancer
- Effect of cancer treatment
- Determining cancer recurrence

Disadvantages of CEA as a Tumour marker
1. CEA, though a broad screening marker, is generally not recommended in preventive screening programmes especially in an asymptomatic individual.
2. The diagnostic efficacy of CEA in the high risk group in a population is not yet established.
3. CEA levels although are included as a part of screening programme but cannot be considered as a definitive marker for malignancy.
4. Chances of false positive and negative results are high and hence in order to decipher the exact stage of disease, the test needs to be repeated at regular intervals.

CEA test at Thyrocare Serum CEA levels in Thyrocare is measured by the advanced Chemiluminescence Immunoassay (CLIA) technology Till now more than 30 tumour markers have been identified and linked to different cancers. However, their role in diagnosis of cancer in the initial stages is still limited, as their serum levels are generally low. Whatever may be the case, serum biomarkers have emerged to be one of the principle diagnostic recommendations of oncologists, as these are easier to detect and the time taken is also less as compared to other tools available for testing. These tests ensure rapid screening for cancer and also help to understand the treatment efficacy.

Thus, CEA though a broad spectrum tumour marker, is still a popularly used follow-up test post treatment of colorectal cancer than screening.