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.
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.
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.
- Screening for cancers: No screening test is wholly specific, and a high level of tumor marker can still be found in benign tumors. One tumor marker used in screening is PSA (prostate-specific antigen).
- Diagnostics: Tumor markers alone can't be used for diagnostic purposes, due to lack of sensitivity and specificity. The only approved diagnostic method for cancer is with a biopsy.
- Detects reoccurring cancers: Tumor markers can detect reoccurring cancers in patients post-treatment.
Interlaboratory proficiency testing for tumor marker tests, and for clinical tests more generally, is routine in Europe and an emerging field in the United States. New York state is prominent in advocating such research.
List of commonly used markers
{|class="wikitable"
! Tumor marker !! Associated tumor types
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| Alpha fetoprotein (AFP) || germ cell tumor, hepatocellular carcinoma
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| CA15-3 || breast cancer
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| CA27.29 || breast cancer
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| CA19-9 || Mainly pancreatic cancer, but also colorectal cancer and other types of gastrointestinal cancer.
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| CA-125 || Mainly ovarian cancer, but may also be elevated in for example endometrial cancer, fallopian tube cancer, lung cancer, breast cancer and gastrointestinal cancer.
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| Calcitonin || medullary thyroid carcinoma
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| Calretinin || mesothelioma, sex cord-gonadal stromal tumor, adrenocortical carcinoma, synovial sarcoma
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| Cytokeratin || Many types of carcinoma, some types of sarcoma
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| thyroglobulin (Tg) || post-operative marker of thyroid cancer (but not in medullary thyroid cancer) Breast cancer, renal cell carcinoma lung cancer, pancreatic cancer, esophageal cancer, stomach cancer, ovarian cancer,
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| vimentin || sarcoma, renal cell carcinoma, endometrial cancer, lung carcinoma, lymphoma, leukemia, melanoma