tumor marker
(TOO-mer MAR-ker)
A substance
found in tissue, blood, bone marrow, or other body fluids
that may be a sign of cancer or certain benign (noncancer)
conditions. Many 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 or RNA, are also being used as
tumor markers. A tumor marker may be used with other tests
to help diagnose cancer. It may also be used to help plan
treatment, give a likely prognosis, and find out how well
treatment is working or if cancer has come back. Examples
of tumor markers include CA-125 (in ovarian cancer),
estrogen receptor and progesterone receptor (in breast
cancer), CEA (in colon cancer), PCA3 mRNA and PSA (in
prostate cancer), and EGFR gene mutation (in non-small cell
lung cancer).