What are they?
Tumour markers are substances, usually proteins, produced by the body in response to cancer growth or by cancer tissue itself. Their detection and measurement in blood plasma, urine or tissue can help to detect and aid diagnosis of some types of cancer, predict and monitor response to treatment and detect recurrence. Recently advances have allowed mutations in cell genetic material (DNA, RNA) to be used as tumour markers to help diagnosis and to determine the prognosis and guide targeted treatment of a few cancers. Research in progress on tumour markers includes analysis of cell-free RNA released into the circulation by cancers and on methods of trapping circulating intact cancer cells for genetic investigation.
Some limitations of tumour markers are that
- none has sufficiently high sensitivity and specificity to be used to screen the general population
- few are specific for one type of cancer
- many are raised in non-cancerous conditions
- not all patients with a cancer of one type have raised concentrations in the bloodstream of its specific tumour marker
- some cancers have no associated tumour marker
Consequently, they cannot be used alone to diagnose cancer but must be considered in conjunction with a patient's medical history, physical examination and other laboratory and imaging tests. A definitive diagnosis of cancer is made by examining a biopsy specimen under a microscope.