Tumour Markers

Why are they done?

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 treatments 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. 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.)