A tumor marker is a biomarker that can be used to indicate the presence of cancer or the behavior of cancers (measure progression or response to therapy). They can be found in bodily fluids or tissue. Markers can help with assessing prognosis, surveilling patients after surgical removal of tumors, and even predicting drug-response and monitor therapy.[1]
Tumor markers can be molecules that are produced in higher amounts by cancer cells than normal cells, but can also be produced by other cells from a reaction with the cancer.[2]
The markers can't be used to give patients a diagnosis but can be compared with the result of other tests like biopsy or imaging.[2]