Definition

A test that measures the amount of substances called tumor markers in tissue, blood, urine, or other body fluids. Most tumor markers are proteins made by both normal cells and cancer cells, but they are made in higher amounts by cancer cells. Genetic changes in tumor tissue, such as gene mutations, patterns of gene expression, and other changes in tumor DNA, are also being used as tumor markers. A tumor marker test is usually done with other tests, such as biopsies or imaging, to help diagnose some types of cancer. It may also be used to help plan treatment or find out how well treatment is working, give a likely prognosis, or find out if cancer has come back or spread to other parts of the body.