What are they?
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 the UK 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 Organisation recommended ten principles be followed when countries consider developing national screening programmes. The essence of these is that the disease should be important, well understood and be able to be recognized 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 itself 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 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 (currently in development).