Understanding Cancer Tests

By Mayer, Deborah K RN, MSN, AOCN®, FAAN

Doctors use tests like mammography, magnetic resonance imaging (MRI), and computed tomography (CT) scans to help them screen for, diagnose, treat, and monitor cancer. If you have been diagnosed with cancer, you may have had one or more of these tests. You may have wondered why you had specific tests and not others or what exactly the doctor was looking for.

Why Do I Need to Be Tested?

There are several reasons why a doctor may order a test for you. Tests may be done to:

  • Screen for cancer. Screening tests are done in people without any symptoms as a way to find a cancer early. An example of this is the Pap smear to screen for cervical cancer or a mammogram for breast cancer.

  • Help diagnose and stage the cancer. If your doctor suspects that you may have cancer, he or she may recommend a test to help diagnose and stage the cancer (find out how far it has spread). An example of this might be a chest x-ray and CT for someone with symptoms suggesting lung cancer.

  • Guide treatment for the cancer. These tests may be used during treatment to help guide or direct the surgery or radiation that is being performed. An example of this might be MRI-guided brain surgery. In this surgery, an MRI is used to create virtual images that help the surgeon remove the tumor with less damage to the surrounding tissues.

  • Monitor the cancer and its treatment. If you have been diagnosed with cancer or if you have had treatment for cancer, your doctor will use tests to monitor the cancer, see if it has come back, or to check for side effects of the treatment. An example of this might be checking the prostatic specific antigen (PSA) levels in someone who has been treated for prostate cancer.

What Type of Tests Exist?

There are different types of tests. Some tests require you to give a sample of your blood, urine, or tissues while others are done on you (for example, an x-ray or CT scan). Usually, more than one test is done to diagnose and monitor cancer. Many of these tests are not cancer specific, but some are.

Tumor Markers

The cancer or the body's response to the cancer may make substances that can be measured. They may be specific to one or more types of cancer or they may be caused by benign problems. Some of these markers are used more in monitoring during and after treatment. Here are some common molecular markers:

Selected Tumor Markers

Cancers linked with increased levels

Alpha-fetoprotein (AFP)

Liver or germ cell cancers of the ovary or testicle

CA 15-3

Advanced breast cancer

CA 19-9

Colorectal, pancreatic, or other gastrointestinal cancers

CA 27-29

Breast cancer

CA 125

Ovarian cancer

Carcinoembryonic antigen (CEA)

Colorectal cancer

Human chorionic gonadotropin (HCG)

Choriocarcinoma (a rare type of uterine cancer) and other cancers

Lactate dehydrogenase (LDH)

A variety of cancers

Neurospecific enolase (NSE)

Neuroblastoma and small cell lung cancer

Prostate-specific antigen (PSA)

Prostate cancer

Prostatic acid phosphatase (PAP)

Prostate cancer

Molecular tumor markers may be measured in blood, urine, or tissue tests and are used along with other tests to diagnose and monitor treatment. Other blood, urine, and other body fluids and tissue tests may be done as well.

Imaging Tests

Imaging tests are used to locate the cancer within the body. This information is helpful in determining the stage of the cancer and help target the cancer treatment to the area where the cancer is located. Here are some common imaging tests.

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