Tumour markers Q&As

What is the CEA test ?

CEA stands for carcinoembryonic antigen. CEA is a protein found at low levels in the blood. A test involves taking blood from a vein to measure the levels of CEA.

With some types of cancer, such as cancers of the bowel, levels of CEA may be higher than normal. Other cancers that may cause higher levels of CEA include cancers of the lung, pancreas, stomach, ovaries, breast and thyroid.

Because CEA is raised in some types of cancer it is called a tumour marker. But, there can be other causes for a raised CEA level. Smokers tend to have higher levels than non-smokers. Non-cancerous conditions that cause inflammation such as pancreatitis, cirrhosis of the liver and bowel diseases can also raise levels above normal.

What is the normal level for CEA?

It isn't possible to give an exact number for this. The figure may differ from one laboratory to another depending on how each laboratory carries out the test. A person's age, sex and whether they are a smoker can also affect what the normal levels for CEA are for them.

Your doctor will be able to tell you what the normal levels for CEA are in the laboratory they use. This should help you to understand your test results better.

Can you tell me what is meant by 'free' and 'bound' PSA?

PSA (prostate specific antigen) exists in the blood in three main forms:

• Free PSA, which is not attached to any other proteins
• Bound PSA which is attached to another protein. These proteins may be either :
• a-antichymotrypsin. (This accounts for the majority of PSA circulating in the blood stream). Or
• a-2 macroglobulin.

The normal tests measuring PSA levels in the blood cannot detect PSA that is bound to a2 macroglobulin, and so gives the total of the free PSA and the PSA bound to a-antichymotrypsin.

Studies have shown that in men with prostate cancer the level of free PSA is less than in men who do not have cancer. So it has been suggested that measuring the ratio of free PSA to the total PSA concentration could help in deciding whether small increases in the PSA level in the blood are due to benign (non-cancerous) prostate disease or prostate cancer.

At the present time, however, there are variations between the different methods available for measuring PSA and uncertainty over what value for the 'free to total' ratio clearly indicates the presence of a cancer. This means that this test is not routinely used in the diagnosis of prostate disease and it is only really appropriate to use it when the PSA level is borderline, although it may become more valuable in the future.

Can you tell me something about tumour markers in testicular cancer?

Some cancers produce abnormal levels of proteins which can be detected in the blood by quite simple blood tests. These proteins are called tumour markers.

Three useful tumour markers have been discovered for testicular cancer. These are alpha-fetoprotein (AFP), human chorionic gonadotrophin (HCG and lactic dehydrogenase (LDH).

There are two main types of testicular cancer: seminomas and teratomas.

Usually any man suspected of having a testicular cancer will have blood taken, to look for tumour markers, before the abnormal testicle is removed.

Three quarters of all teratomas produce abnormally high blood levels of HCG and/or AFP. Measuring the blood level of HCG and AFP before surgery, and monitoring how quickly those levels fall after the testicle has been removed, gives important information about the aggressiveness of the tumour, the possible risk of any spread to other parts of the body and the likely need for any further treatment.

At later check-ups blood tests will usually be taken to check the HCG and AFP levels. If the tumour markers start to increase then this is a strong indication that the cancer is recurring elsewhere in the body and further treatment will be needed. The blood levels of the markers can then be used to check that the treatment (usually chemotherapy) is working.

Tumour markers are less helpful in seminomas. Only about one third of seminomas produce HCG, and the increase in blood level is usually quite small. Seminomas do not produce AFP.

LDH is often produced when both teratomas and seminomas have spread to other parts of the body. In this situation LDH measurements can be used to help check on the progress of treatment - a falling blood level showing that the chemotherapy is working.

Why can't the CEA test be used to screen for bowel cancer?

CEA is a protein found in blood. Blood levels of CEA are often raised in people with cancer of the bowel. But, testing for CEA isn't a good way of screening for bowel cancer. (Screening means testing to find a cancer at an early stage, before there are any symptoms.)

There are 2 main reasons why the CEA test can't be used to screen for bowel cancer:

It's not sensitive enough

Not everyone with bowel cancer has high levels of CEA. So, a negative CEA test can't rule out bowel cancer.

When CEA levels rise because of a bowel cancer, the cancer has often been developing for sometime. So, measuring CEA levels isn't a good way of detecting bowel cancer early on.

It's not specific enough

CEA levels can be raised by non-cancerous conditions like inflammation, infections and bowel disease. Because of this, many people with a high CEA level don't have cancer. So, if CEA levels were used to screen for cancer many people would have invasive tests they didn't need, such as a colonoscopy.