Cancer Screening Tests: The Basics
What is a screening test?
Cancer screening tests look 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.
There are different kinds of screening tests
Screening tests can include the following:
- 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 detect breast lumps or masses.
- Laboratory tests: Samplings of tissue, blood, urine, or other things in the body. For example, a blood test that measures PSA (prostate specific antigen) is used to screen for prostate cancer
- Imaging procedures: Take pictures of areas inside the body, such as a mammogram, a screening test for breast cancer.
What Makes a Good Screening Test?
A good screening test is a safe test
A screening test should pose very little risk to patients. The more invasive a test is, the higher the risk. For example, a colonoscopy (uses anesthesia, may take biopsy) has a low risk of side effects, but 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 really 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 undue stress, anxiety, and can lead to other unnecessary testing. False-negative results can delay treatment.
Understanding Sensitivity and Specificity
The terms used to describe how good a screening test is are sensitivity and 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 best screening tests have high sensitivity and high specificity.
The Limitations of Screening Tests
Unfortunately, not every type of cancer has a good screening test. Most screening tests have some false positive results. These cause unnecessary stress and anxiety for the patient. They also result in further testing, which can have risks and can be costly. All to find out there was nothing wrong.
Not every cancer is detected with a screening test (called false negative results). This causes a delay in the person finding out they have cancer and a delay in treatment. This can result in treatment not being as successful.
If signs of cancer are detected on a screening test, more tests are performed to confirm the diagnosis. Controversy arises when it is not clear if the benefits of screening outweigh the risks of follow-up diagnostic tests and cancer treatments. Ultimately, whether or not you have a particular screening test is something you should decide with your doctor after discussing 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.
- Benefits and risks of screening tests. Pub Med Health. Found at https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072602/
- Cancer Screening from the National Cancer Institute. https://www.cancer.gov/about-cancer/screening
- Information about various cancer screening tests from the American Cancer Society. https://www.cancer.org/healthy/find-cancer-early/cancer-screening-tests-videos.html