Cancer Screening Tests: The Basics

What is a screening test?

A cancer screening test looks for cancer before a person has any symptoms. When abnormal tissue or cancer is found early, it may be easier to treat or cure. By the time symptoms appear, the cancer may be more advanced and could be harder to treat or cure.

Why do a screening test?

Screening tests are used for types of cancer that are common in the population; this means the disease has a high incidence rate. Screening tests are also used for diseases where there are good treatments available. If there are no good treatments, screening is not helpful since there isn’t a way to treat the disease if you find it.

When your healthcare provider suggests a screening test, it does not mean they think you have cancer. Screening tests are recommended at certain ages and/or based on your family health history.

What are the types of screening tests?

Screening tests can be:

• Physical exam: An exam of the body to check your health, including checking for signs of disease. An example is a breast exam done to check for breast lumps or masses.
• Laboratory tests: Samplings of tissue, blood, urine, or other things in the body are tested. For example, a blood test that measures PSA (prostate specific antigen) is used to screen for prostate cancer
• Imaging: Pictures are taken of areas inside the body, like a mammogram, which is a screening test for breast cancer.

What makes a good screening test?

A good screening test is safe. A screening test has very little risk to patients. The more invasive or complicated a test is, the higher the risk. For example, a colonoscopy (uses anesthesia, may take biopsy) has a low risk of side effects but has a higher risk than a simple blood test.

A good screening test gives useful results. This means the test should be reliable in finding the disease when it is present in the patient AND find no disease if it is not present. A false-positive test occurs when test results appear to be abnormal, even though there is actually no cancer. A false-negative is when test results show no cancer when there actually is cancer.

No test is perfect. A perfect test would give only true positive and true negative results, but a good screening test should have a low rate of false-positive and false-negative results. False-positive results can create stress, anxiety, can lead to unnecessary testing, and delay treatment.

Understanding Sensitivity and Specificity

Sensitivity and specificity are the terms used to describe how good a screening test is. The best screening tests have both high sensitivity and high specificity.

• Sensitivity is the "true positive rate." The closer the sensitivity is to 100%, the more likely that a positive result actually means that the patient has a disease.
• Specificity is the "true negative rate." The closer the specificity is to 100%, the more likely a negative result means that the patient is truly disease-free.

The Limitations of Screening Tests

Not every type of cancer has a good screening test. Most screening tests have some false-positive results. These can cause unnecessary stress and anxiety. They also result in more testing, which can have risks and can be costly.

Not every cancer is detected (found) with a screening test (false-negative results). This causes a delay in the cancer being found and a delay in treatment. Because of the delay, this can result in treatment not being as successful.

If signs of cancer are seen on a screening test, more tests are done to confirm the diagnosis. Sometimes it is not clear if the benefits of screening outweigh the risks of follow-up diagnostic tests and cancer treatments. Whether or not you have a screening test is something you should decide with your care team after talking about your risk factors and personal preferences.

Learn more about cancer screening tests for men on OncoLink.

Learn more about cancer screening tests for women on OncoLink.