Tumor Markers: Questions and Answers 

Key Points

• Tumor markers are substances that can be found in abnormal amounts in the 

blood, urine, or tissues of some patients with cancer (see Question 1). 

• Different tumor markers are found in different types of cancer (see Question 1). 

• Tumor markers may be used to help diagnose cancer, predict a patient’s 

response to particular therapies, check a patient’s response to treatment, or 

determine if cancer has returned (see Questions 3 and 4). 

• In general, tumor markers cannot be used alone to diagnose cancer; they must 

be combined with other tests (see Question 3). 

• Researchers continue to study tumor markers and to develop more accurate 

methods to detect, diagnose, and monitor cancer (see Question 7). 

1. What are tumor markers?

Tumor markers are substances produced by tumor cells or by other cells of the body in 

response to cancer or certain benign (noncancerous) conditions. These substances can be 

found in the blood, in the urine, in the tumor tissue, or in other tissues. Different tumor 

markers are found in different types of cancer, and levels of the same tumor marker can 

be altered in more than one type of cancer. In addition, tumor marker levels are not 

altered in all people with cancer, especially if the cancer is early stage. Some tumor 

marker levels can also be altered in patients with noncancerous conditions. 

To date, researchers have identified more than a dozen substances that seem to be 

expressed abnormally when some types of cancer are present. Some of these substances 

are also found in other conditions and diseases. Scientists have not found markers for 

every type of cancer. 

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2. What are risk markers? 

Some people have a greater chance of developing certain types of cancer because of a 

change, known as a mutation or alteration, in specific genes. The presence of such a 

change is sometimes called a risk marker. Tests for risk markers can help the doctor to 

estimate a person’s chance of developing a certain cancer. Risk markers can indicate that 

cancer is more likely to occur, whereas tumor markers can indicate the presence of cancer 

(1). 

 

3. How are tumor markers used in cancer care?

Tumor markers are used in the detection, diagnosis, and management of some types of 

cancer. Although an abnormal tumor marker level may suggest cancer, this alone is 

usually not enough to diagnose cancer. Therefore, measurements of tumor markers are 

usually combined with other tests, such as a biopsy, to diagnose cancer. 

Tumor marker levels may be measured before treatment to help doctors plan appropriate 

therapy. In some types of cancer, tumor marker levels reflect the stage (extent) of the 

disease. (More information about staging is available in the National Cancer Institute 

(NCI) fact sheet Staging: Questions and Answers, which can be found at 

http://www.cancer.gov/cancertopics/factsheet/Detection/staging on the Internet.) 

Tumor marker levels also may be used to check how a patient is responding to treatment. 

A decrease or return to a normal level may indicate that the cancer is responding to 

therapy, whereas an increase may indicate that the cancer is not responding. After 

treatment has ended, tumor marker levels may be used to check for recurrence (cancer 

that has returned). 

4. How and when are tumor markers measured?

The doctor takes a blood, urine, or tissue sample and sends it to the laboratory, where

various methods are used to measure the level of the tumor marker.

If the tumor marker is being used to determine whether a treatment is working or if there 

is recurrence, the tumor marker levels are often measured over a period of time to see if 

the levels are increasing or decreasing. Usually these “serial measurements” are more 

meaningful than a single measurement. Tumor marker levels may be checked at the time 

of diagnosis; before, during, and after therapy; and then periodically to monitor for 

recurrence. 

5. Does the NCI have guidelines for the use of tumor markers? 

No, the NCI does not have such guidelines. However, some organizations do have these 

guidelines for some types of cancer. 
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The American Society of Clinical Oncology (ASCO), a nonprofit organization that 

represents more than 25,000 cancer professionals worldwide, has published clinical 

practice guidelines on a variety of topics, including tumor markers for breast and 

colorectal cancer. These guidelines, called Patient Guides, are available on the ASCO 

Web site at http://www.cancer.net/patient/ASCO+Resources/Patient+Guides on the 

Internet. 

The National Comprehensive Cancer Network® (NCCN), which is also a nonprofit 

organization, is an alliance of cancer centers. The NCCN provides Patient Guidelines, 

which include tumor marker information for several types of cancer. Most of the 

guidelines are available in English and Spanish versions. The Patient Guidelines are on 

the NCCN’s Web site at http://www.nccn.org/patients/patient_gls.asp on the Internet. 

The National Academy of Clinical Biochemistry (NACB) is a professional organization 

dedicated to advancing the science and practice of clinical laboratory medicine through 

research, education, and professional development. The Academy publishes Practice 

Guidelines and Recommendations for Use of Tumor Markers in the Clinic, which focuses 

on the appropriate use of tumor markers for specific cancers. More information can be 

found at http://direct.aacc.org/ProductCatalog/Product.aspx?ID=2131 on the Internet. 

6. Can tumor markers be used as a screening test for cancer?

Screening tests are a way of detecting cancer early, before there are any symptoms. For a 

screening test to be helpful, it should have high sensitivity and specificity. Sensitivity 

refers to the test’s ability to identify people who have the disease. Specificity refers to 

the test’s ability to identify people who do not have the disease. Most tumor markers are 

not sensitive or specific enough to be used for cancer screening. 

Even commonly used tests may not be completely sensitive or specific. For example, 

prostate-specific antigen (PSA) levels are often used to screen men for prostate cancer, 

but this is controversial. It is not yet known if early detection using PSA screening 

actually saves lives. Elevated PSA levels can be caused by prostate cancer or benign 

conditions, and most men with elevated PSA levels turn out not to have prostate cancer. 

Moreover, it is not clear if the benefits of PSA screening outweigh the risks of follow-up 

diagnostic tests and cancer treatments. (More information about PSA screening is 

available in the NCI fact sheet The Prostate-Specific Antigen (PSA) Test: Questions and 

Answers, which can be found at 

http://www.cancer.gov/cancertopics/factsheet/Detection/PSA on the Internet.) 

Another tumor marker, CA 125, is sometimes used to screen women who have an 

increased risk for ovarian cancer. Scientists are studying whether measurement of 

CA 125, along with other tests and exams, is useful to find ovarian cancer before 

symptoms develop. So far, CA 125 measurement is not sensitive or specific enough to be 

used to screen all women for ovarian cancer. Mostly, CA 125 is used to monitor 

response to treatment and check for recurrence in women with ovarian cancer. 
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7. What research is being done in this field? 

Scientists continue to study tumor markers and their possible role in the early detection 

and diagnosis of cancer. The NCI is currently conducting the Prostate, Lung, Colorectal, 

and Ovarian Cancer screening trial, or PLCO trial, to determine if certain screening tests 

reduce the number of deaths from these cancers. Along with other screening tools, PLCO 

researchers are studying the use of PSA to screen for prostate cancer and CA 125 to 

screen for ovarian cancer. Final results from this study are expected in several years. 

Cancer researchers are turning to proteomics (the study of protein shape, function, and 

patterns of expression) in hopes of developing better cancer screening and treatment 

options. Proteomics technology is being used to search for proteins that may serve as 

markers of disease in its early stages or to predict the effectiveness of treatment or the 

chance of the disease returning after treatment has ended. More information about 

proteomics can be found in Proteomics and Cancer: Fact Sheet, which is available at 

http://www.cancer.gov/cancertopics/factsheet/proteomicsqa on the Internet. 

Scientists are also evaluating patterns of gene expression (the step required to translate 

what is in the genes to proteins) for their ability to predict a patient’s prognosis (likely 

outcome or course of disease) or response to therapy. NCI’s Early Detection Research 

Network is developing a number of genomic- and proteomic-based biomarkers, some of 

which are being validated. More information about this program can be found at 

http://edrn.nci.nih.gov/ on the Internet. 

Information about clinical trials is available from the NCI’s Cancer Information Service 

(see below) or on the clinical trials page of the NCI’s Web site at 

http://www.cancer.gov/clinicaltrials on the Internet. In addition, PDQ®, the NCI’s 

comprehensive cancer information database, contains cancer information summaries that 

can be found at http://www.cancer.gov/cancerinfo/pdq/ on the Internet. 

Selected Reference 

1. Bigbee W, Herberman RB. Tumor markers and immunodiagnosis. In: Bast RC Jr., 

Kufe DW, Pollock RE, et al., editors. Cancer Medicine. 6th ed. Hamilton, Ontario, 

Canada: BC Decker Inc., 2003. 

# # # 

Related NCI materials and Web pages: 

• National Cancer Institute Fact Sheet 3.62, Genetic Testing for BRCA1 and BRCA2: 

It’s Your Choice (http://www.cancer.gov/cancertopics/factsheet/Risk/BRCA) 

• National Cancer Institute Fact Sheet 5.27, Interpreting Laboratory Test Results

(http://www.cancer.gov/cancertopics/factsheet/Detection/laboratory-tests) 
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• National Cancer Institute Fact Sheet 5.29, The Prostate-Specific Antigen (PSA) Test: 

Questions and Answers

(http://www.cancer.gov/cancertopics/factsheet/Detection/PSA) 

• National Cancer Institute Fact Sheet 5.32, Staging: Questions and Answers

(http://www.cancer.gov/cancertopics/factsheet/Detection/staging) 

• National Cancer Institute Fact Sheet 8.2, Understanding Prognosis and Cancer 

Statistics: Questions and Answers

(http://www.cancer.gov/cancertopics/factsheet/support/prognosis-stats) 

• What You Need To Know AboutTM Cancer—An Overview

(http://www.cancer.gov/cancertopics/wyntk/overview) 

For more help, contact: 

NCI’s Cancer Information Service 

Telephone (toll-free): 1–800–4–CANCER (1–800–422–6237) 

TTY (toll-free): 1–800–332–8615

LiveHelp® online chat: https://cissecure.nci.nih.gov/livehelp/welcome.asp

This fact sheet was reviewed on 2/3/06