Tumor Markers

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Tumor markers found on the cancer itself

These tumor markers are usually checked at diagnosis, or shortly after a biopsy confirms cancer. This type of test requires a tissue sample that includes cancer cells, which is usually harder to get than blood or urine. Since cancer cells themselves are being tested, it’s typically a one-time test result. The information is often used to further identify the cancer or to help choose a treatment.

Anaplastic lymphoma kinase (ALK)

Some lung cancers have changes in the ALK gene that cause the cancer cell to make a protein that leads to out-of-control growth. Tumor tissues can be tested for this gene change. If it’s found, the patient can be treated with a drug that targets the abnormal protein, like crizotinib (Xalkori®).


Defects (mutations) in the BRAF gene can be found in melanoma, thyroid cancer, and colorectal cancer. About half of melanomas have a BRAF mutation, most often the one called BRAF V600. This mutation causes the gene to make an altered BRAF protein that signals melanoma cells to grow and divide. This mutation can be tested for in tumor tissue. If it’s found, the patient can be treated with a drug that targets the altered BRAF protein, such as vemurafenib (Zelboraf®).

Colorectal cancers that have BRAF mutations aren’t helped by drugs that target the epidermal growth factor receptors (see below). Doctors typically check tumor tissue to be sure it doesn’t have BRAF mutations before starting patients on these drugs.

Some melanomas have different BRAF mutations. These melanomas can be treated with a different targeted drug.

BRAF mutations have also been found in some other cancers, including thyroid cancer and lung cancer. So far, though, drugs targeting BRAF mutations are not used to treat these diseases.

Epidermal growth factor receptor (EGFR)

This protein, also known as HER1, is a receptor found on cells that helps them grow. Tests done on a piece of the cancer tissue can look for increased amounts of these receptors, which is a sign that the cancer may grow fast, spread quickly, and be harder to treat. Patients with elevated EGFR may have poorer outcomes and need more aggressive treatment, particularly with drugs that block (or inhibit) the EGFR receptors.

EGFR may be used to guide treatment and predict outcomes of non-small cell lung, head and neck, colon, pancreas, or breast cancers. The results are reported as a percentage based on the number of cells tested.

Some lung cancers have certain defects (mutations) in the EGFR gene that make it more likely that certain drugs will work against the cancer. These gene changes are more common in lung cancer patients who are women, non-smokers, or Asian.

HER2 (or HER2/neu, erbB-2, or EGFR2)

HER2 is a protein that tells some cancer cells to grow. It’s present in larger than normal amounts on the surface of breast cancer cells in about 1 out of 5 people with breast cancer. Higher-than-normal levels can be found in some other cancers, too, such as some stomach and esophageal cancers. HER2 is usually found by testing a sample of the cancer tissue itself. Cancers that are HER2-positive tend to grow and spread faster than other cancers.

All newly diagnosed breast cancers and advanced stomach cancers should be tested for HER2. HER2-positive cancers are more likely to respond to drugs that work against the HER2 receptor on cancer cells.

Hormone receptors

Breast tumor samples from all people with breast cancer are tested for estrogen and progesterone receptors. These 2 hormones often fuel the growth of breast cancer cells. Breast cancers that contain estrogen receptors are often called ER-positive; those with progesterone receptors are PR-positive. About 2 out of 3 breast cancers test positive for at least one of these markers. Hormone receptor-positive breast cancers tend to grow more slowly and may have a better outlook than cancers without these receptors. Cancers that have these receptors can be treated with hormone therapy such as tamoxifen or aromatase inhibitors.

Some gynecologic tumors, such as endometrial cancers and endometrial stromal sarcomas, are also checked for hormone receptors to see if they can be treated with hormone therapy drugs.


Cetuximab (Erbitux®) and panitumumab (Vectibix®) are two drugs that target the EGFR protein and can be useful in the treatment of advanced colorectal cancer. But these drugs don’t work in colorectal cancers that have mutations (defects) in the KRAS gene. Doctors now commonly test the tumor for this gene change and only use these drugs in people whose cancers do not have the mutation.

KRAS mutations can also help guide treatment for some types of lung cancer. For instance, tumors with the mutations do not respond to treatment with drugs erlotinib (Tarceva®) or gefitinib (Iressa®). Doctors are looking at how KRAS may be used in many other types of cancer, too.


S-100 is a protein found in most melanoma cells. Tissue samples (biopsies) of suspected melanomas may be tested for this marker to help in diagnosis. Sometimes, a blood test that detects S-100 is used to look for melanoma spread before, during, or after treatment.

Other tumor marker tests: commercial labs and research studies

Tests for many other tumor markers are available through commercial testing labs, but these are seldom used.

Some of these tests may even be advertised as being better than the more common markers, but this hasn’t yet been shown in scientific studies. In some of these cases, the tests have been taken off the market at the request of the Food and Drug Administration (FDA). Still, there are tests available for many types of cancer that have not yet been proven to work.

Researchers use other tumor markers that are often not available to doctors or hospital labs. If research does show that they are useful, they are then made available to doctors and their patients.

Last Medical Review: 10/30/2013
Last Revised: 10/30/2013