Why are they done?
Tumor markers are not diagnostic in themselves. A definitive diagnosis of cancer is made by looking at tissue biopsy specimens 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 people with a strong family history of a particular cancer. As mentioned, PSA testing may be used to screen for prostate cancer.
- Diagnose. In a person who 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 by themselves but aid in this process.
- Stage. If a person 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. A few 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, since other conditions can sometimes cause tumor markers to rise or fall.
- Determine Recurrence. Currently, one of the most important 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.)