Cancer Marker

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     Tumor Markers

What are they?

Tumor markers are substances, usually proteins, that are produced by the body in response to cancer growth or by the cancer tissue itself. Some tumor markers are specific, while others are seen in several cancer types. Many of the well-known markers are also seen in non-cancerous conditions. Consequently, these tumor markers are not diagnostic for cancer.

There are only a handful of well-established tumor markers that are being routinely used by physicians. 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, the only tumor marker to gain wide acceptance as a general screen is the Prostate Specific Antigen (PSA) for men. Other 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.

Some people are at a higher risk for particular cancers because they have inherited a genetic mutation. While not considered tumor makers, 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. For more information, see our overview on genetic testing.

Why are they done?

Tumor 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, tumor markers provide information that can be used to:

• Screen. Most markers are not suited for general screening, but some may be used in 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. PSA testing for prostate cancer is an example.

• Help diagnose. In a patient that has symptoms, tumor 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 tumor markers cannot diagnose cancer themselves but aid in this process.

• Stage. If a patient does have cancer, tumor marker elevations can be used to help determine how far the cancer has spread into other tissues and organs.

• Determine prognosis. Some tumor markers can be used to help doctors determine how aggressive a cancer is likely to be.

• Guide Treatment. Some tumor markers, such as Her2/neu, will give doctors information about what treatments their patients may respond to (for instance, breast cancer patients who are Her2/neu positive are more likely to respond to Herceptin treatment).

• Monitor Treatment. Tumor 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. CEA, for instance, is used to monitor colorectal cancer, but not every colorectal cancer patient will have elevated levels of CEA.

• Determine recurrence. Currently, one of the biggest uses for tumor markers is to monitor for cancer recurrence. If a tumor 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.)

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