Cancer screening aims to detect cancer before symptoms appear. This may involve blood tests, urine tests, DNA tests other tests, or medical imaging. The benefits of screening in terms of cancer prevention, early detection and subsequent treatment must be weighed against any harms
Potential Benefits of Cancer Screening
In general, the benefit of cancer screening derives from detecting cancer in earlier and more treatable stages, and thereby, reducing mortality from cancer. In addition, for some cancer types and screening modalities, such as endoscopic screening for colorectal cancer and Papanicolaou (Pap) smears for cervical cancer, screening can also prevent the occurrence of cancer by identifying and removing cancer precursors. Screening may also reduce cancer morbidity when the treatment for earlier-stage cancer is associated with fewer side effects than the treatment for advanced cancers.
Certain tests help find specific types of cancer before signs or symptoms appear. This is called screening. The main goals of cancer screening are to:
- Reduce the number of people who die from the disease, or prevent deaths from cancer altogether
- Reduce the number of people who develop the disease
Types of screening tests
Each type of cancer has its own screening tests. Some types of cancer currently do not have an effective screening method. Developing new cancer screening tests is an area of active research.
Mammography is a type of x-ray specifically designed to view the breast. The images produced by mammography can show tumors or irregularities in the breast. These images are called mammograms.
- Clinical breast examination. A medical professional looks and feels for any changes in the breast’s size or shape. The examiner also looks for changes in the skin of the breasts and nipples.
- Breast self-examination. During this exam, a woman looks and feels for changes in her own breasts. If she notices any changes, she should see a doctor.
- Magnetic resonance imaging (MRI). An MRI is not regularly used to screen for breast cancer. But it may be helpful for women with a higher risk of breast cancer, those with dense breasts, or when a lump is found during a breast exam.
Human papillomavirus (HPV) testing. Cells are scraped from the outside of a woman’s cervix. These cells are tested for specific strains of HPV. Some strains of HPV are more strongly linked to an increased risk of cervical cancer. This test may be done alone or combined with a Pap test (see below). An HPV test may also be done on a sample of cells from a woman’s vagina that she can collect herself.
Pap test. This test also uses cells from the outside of a woman's cervix. A pathologist then identifies any precancerous or cancerous cells. A Pap test may be combined with HPV testing.
Colonoscopy. During this procedure, the doctor inserts a flexible, lighted tube called a colonoscope into the rectum. The doctor is able to check the entire colon for polyps or cancer.
Sigmoidoscopy. The doctor uses a flexible, lighted tube called a sigmoidoscope to check the lower colon for polyps and cancer. The doctor cannot check the upper part of the colon with this test.
Fecal occult blood test (FOBT). This test finds blood in the feces, or stool, which can be a sign of polyps or cancer. There are two types FOBT: guaiac and immunochemical.
Double contrast barium enema. This is an x-ray of the colon and rectum. The barium enema helps the outline of the colon and rectum stand out on the x-rays. Doctors use this test to screen people who cannot have a colonoscopy.
Stool DNA tests. This test analyzes DNA from a person’s stool sample to look for cancer. It uses DNA changes found in polyps and cancers to help a doctor decide if a colonoscopy is needed.
Head and neck cancers
General health screening exam. The doctor looks in the nose, mouth, and throat for abnormalities and feels for lumps in the neck. Regular dental check-ups are also important to screen for head and neck cancers.
Low-dose helical or spiral computed tomography (CT or CAT) scan. A CT scan takes x-rays of the inside of the body from different angles. A computer then combines these images into a detailed, 3-dimensional image that shows any abnormalities or tumors.
Learn more about lung cancer screening.
Digital rectal examination (DRE). A DRE is a test in which the doctor inserts a gloved lubricated finger into a man’s rectum and feels the surface of the prostate for any irregularities.
Prostate-specific antigen (PSA) test. This blood test measures the level of a substance called PSA. PSA is usually found at higher-than-normal levels in men with prostate cancer. But a high PSA level may also be a sign of conditions that are not cancerous.
Complete skin exam. A doctor checks the skin for signs of skin cancer.
Skin self-examination. People examine their entire body in a mirror for signs of skin cancer. It often helps to have another person check the scalp and back of the neck.
Dermoscopy. A doctor uses a handheld device to evaluate the size, shape, and pigmentation patterns of skin lesions. Dermoscopy is usually used for the early detection of melanoma.
Risks of screening
Screening tests can help doctors find a cancer at an earlier, more treatable stage. This may help improve survival. But cancer screening also has a number of risks. These risks include:
Overdiagnosis. Screening tests may find slow-growing cancers that would not have caused any harm during a person's lifetime. As a result, some people may receive potentially harmful, painful, stressful, and/or expensive treatments that they did not need.
False positives. Sometimes a screening test will suggest that a person has cancer when they do not.
Increased testing. Doctors may run additional tests that a person may not need because of overdiagnosis and false positives. These tests can be physically invasive, costly, and can cause unnecessary stress and worry.
False reassurance. Sometimes a screening test will suggest a person does not have cancer when they actually do. As a result, a person may not get the treatment he or she needs.
A number of organizations provide guidelines on cancer screening tests. Sometimes these guidelines suggest different things. Recommendations vary on:
- Which type of cancer people should be screened for
- Which tests should be used to screen for a particular type of cancer
- What age screening should begin and end
- How often screening tests should be done
- What happens if the screening shows positive results?
Talk with your doctor about your personal risk of developing cancer. Together you can decide on an appropriate screening schedule based on your age and personal and family medical history.