Tumour markers are substances (often proteins) that are produced by some cancer cells or that are produced by healthy cells in response to the cancer. Such substances are found in higher-than-normal concentrations in the blood, urine, or tissues of people with those cancers that give rise to the production of tumour markers, as not all cancers do. These days it is also possible to map genetic changes (changes in the genes of people with cancer) and to use these as tumour markers. [1]
Tumour markers are not used in isolation to diagnose or stage cancer but are combined with other special investigations to formulate treatment plans and assist with staging. In some instances, they may be used for screening purposes in a person with a high risk of getting cancer (e.g., due to family history) before the onset of symptoms or signs of cancer. Mostly, however, tumour markers are used to:
Not all tumours produce tumour markers so testing of tumour markers is not necessarily an option for all cancers. [1]
It is important to understand that there are different types of tumour markers for different cancers and there is no one size fits all. Certain tumour markers are specific to only one type of cancer, while other tumour markers may be associated with more than 1 cancer. It is an evolving field of cancer medicine with researchers continuing to search for new and more effective markers. [1]
Levels of tumour markers are usually determined by performing blood, stool, or urine tests. Sometimes a biopsy is required. This will require the removal of a piece of the cancerous tissue with the use of a needle or with a surgical incision. The tissue will then be examined in a laboratory. Sometimes levels of tissue markers are measured repeatedly to determine response to treatment or to see whether cancer has returned. [1,2]
Examples of tumour markers in common use are alpha-fetoprotein for liver cancer and germ cell tumours, beta-2 microglobulin for some types of blood cancer and lymphoma (cancer of the lymphatic system), bladder tumour antigen (BTA) for bladder cancer and cancer of the kidney or ureter, and BRCA1 and BRCA2 gene mutations for breast and ovarian cancer. There are many more such tumour markers. [3]
There are limitations to the use of tumour markers. It has already been mentioned that not all tumours produce tumour markers. For those that do, levels may fluctuate over time so it is difficult to measure them consistently. Also, even for tumours known to produce tumour markers, it sometimes happens that, in a specific individual, the blood, urine or tissue levels of the marker are within normal limits, even though cancer is present. [1]
Tumour marker tests thus can provide both false-positive and false-negative results. A false-positive result is where the levels of the tumour marker are elevated, but the person does not have cancer. A false-negative result is where the levels are within the normal limits, but cancer is present. When it comes to making decisions about treatment, response to treatment or cancer recurrence, doctors will not rely solely on the results of tumour marker tests but will always interpret them in conjunction with the results of the other special investigations. [1,3]
Tumour markers are substances produced by cancer cells or by normal cells in response to cancer. Different cancers produce different markers and, while some tumour markers are specific to certain cancer, other tumour markers may be associated with more than one cancer. Although never used in isolation, tumour markers are used to assist with treatment planning and to evaluate response to treatment. They also provide useful information about prognosis and can be utilised to detect cancer recurrence.