What is being tested?

Tumour markers are substances, usually proteins, that are produced by the body in response to cancer growth or by the cancer tissue itself. Some tumour markers are specific for one type of cancer, while others are seen in several cancer types. Many of the well-known markers are seen in non-cancerous conditions as well as cancer. Consequently, they cannot be used to diagnose cancer.

There are only a handful of well-established tumour markers that are being routinely used by doctors. Many other potential markers are still being researched. Some marker tests cause great excitement when they are first discovered but, upon further investigation, prove to be no more useful than markers already in use.

The goal is to be able to screen for and diagnose cancer early, when it is the most treatable and before it has had a chance to grow and spread. So far, no tumour marker has gained acceptance in Australia as a general screen, including the prostate specific antigen (PSA) for men. The markers are either not specific enough (too many false positives, leading to expensive and unnecessary follow-up testing) or they are not elevated early enough in the disease process.

In 1968 the World Health Organization recommended ten principles to be followed when countries consider developing national screening programs. The essence of these is that the disease should be important, well understood and be able to be recognised and tested for at an early stage. Medical support and treatment must be available and be more beneficial if given at an early stage. The health benefits must be greater than any harm done by the screening process which also must be cost effective.

Some people are at a higher risk for particular cancers because they have inherited a genetic mutation. While not considered tumour markers, there are tests that look for these mutations in order to estimate the risk of developing a particular type of cancer. BRCA1 and BRCA2 are examples of gene mutations related to an inherited risk of breast cancer and ovarian cancer.

When is it requested?

Tumour markers are not diagnostic in themselves. A definitive diagnosis of cancer is made by looking at biopsy specimens (e.g., of tissue) under a microscope. However, tumour markers provide information that can be used to:

• Monitor. While at present no markers are suited for general screening, some may be used to monitor those with a strong family history of a particular cancer. In the case of genetic markers, they may be used to help predict risk in family members.
• Help diagnose. In a patient that has symptoms, tumour markers may be used to help identify the source of the cancer, such as CA-125 for ovarian cancer, and to help differentiate it from other conditions. Remember that tumour markers cannot diagnose cancer themselves but aid in this process.
• Stage. If a patient does have cancer, tumour marker elevations can be used to help determine how far the cancer has spread into other tissues and organs.
• Determine prognosis. Some tumour markers can be used to help doctors determine how aggressive a cancer is likely to be.
• Guide treatment. Some tumour markers, such as Her2/neu, will give doctors information about what treatment their patients may respond to (for instance, breast cancer patients who are Her2/neu positive are more likely to respond to Herceptin therapeutic drug treatment).
• Monitor treatment. Tumour markers can be used to monitor the effectiveness of treatment, especially in advanced cancers. If the marker level drops, the treatment is working; if it stays elevated, adjustments are needed. The information must be used with care, however. Carcinoembryonic antigen (CEA), for instance, is used to monitor bowel cancer, but not every bowel cancer patient will have elevated levels of CEA. If the marker level is not initially elevated with the cancer, it cannot be used later as a monitoring tool.
• Determine recurrence. Currently, one of the biggest uses for tumour markers is to monitor for cancer recurrence. If a tumour marker is elevated before treatment, low after treatment and then begins to rise over time, then it is likely that the cancer is returning. (If it remains elevated after surgery, then chances are that not all of the cancer was removed.)

Common tumour markers currently in use

Other tumour markers less widely used

More Information

RCPA Manual: Tumour markers