A test that measures the amount of substances called tumor markers in tissue, blood, urine, or other body fluids. Most tumor markers are made by both normal cells and cancer cells, but they are made in higher amounts by cancer cells. A high level of a tumor marker may be a sign of cancer or certain benign (noncancerous) conditions. A tumor marker test is usually done with other tests, such as biopsies, to help diagnose some types of cancer. It may also be used to help plan treatment or find out how well treatment is working or if cancer has come back.