The presence of certain substances in the blood can indicate you might have certain cancers but this is not always the case. Doctors also use these markers to assess other things related to cancer. The National Institute of Cancer and the American Cancer Society offer guidelines regarding cancer markers in blood tests.
Tumour markers are substances that might form as a result of cancer or are normally found in the blood but at elevated levels. They tend to be proteins. The cancer might produce them or your body might produce the markers in response to the cancer.
While certain cancers produce or elevate certain substances in the blood, this alone cannot determine if you have cancer. Non-cancerous cells as well as conditions and diseases other than cancer can produce similar results. Not everyone with a certain type of cancer will have markers. You typically require other tests to confirm a diagnosis. Tumour markers can also determine the site of the primary cancer when it is diagnosed at an advanced stage.
Doctors test blood tumour markers to determine the most appropriate treatments and to assess the effects of your current therapy. If the markers go down the treatments are working; if they rise, he will consider other options.
Tumour markers can indicate the aggressiveness of the tumour--meaning how quickly it might spread. This can assist in prognosis.
If you go into remission, you will need regular testing to see if your cancer has come back. Tumour marker testing for this purpose typically applies to cancers of the colon, rectum, prostate, liver, ovaries and some germ cell cancers.