Screening tests have risks.

Decisions about screening tests can be difficult. Not all screening tests are helpful and most have risks. Before having any screening test, you may want to discuss the test with your doctor. It is important to know the risks of the test and whether it has been proven to reduce the risk of dying from cancer.

The risks of breast cancer screening tests include the following:

Finding breast cancer may not improve health or help a woman live longer.

Screening may not help you if you have fast-growing breast cancer or if it has already spread to other places in your body. Also, some breast cancers found on a screening mammogram may never cause symptoms or become life-threatening. When such cancers are found, treatment would not help you live longer and may instead cause serious treatment-related side effects. At this time, it is not possible to be sure which breast cancers found by screening will cause symptoms and which breast cancers will not.

False-negative test results can occur.

Screening test results may appear to be normal even though breast cancer is present. A woman who receives a false-negative test result (one that shows there is no cancer when there really is) may delay seeking medical care even if she has symptoms.

One in 5 cancers may be missed by mammography. False-negatives occur more often in younger women than in older women because the breast tissue of younger women is more dense. The size of the tumor, the rate of tumor growth, the level of hormones, such as estrogen and progesterone, in the woman’s body, and the skill of the radiologist can also affect the chance of a false-negative result.

False-positive test results can occur.

Screening test results may appear to be abnormal even though no cancer is present. A false-positive test result (one that shows there is cancer when there really isn’t) can cause anxiety and is usually followed by more tests (such as biopsy), which also have risks.

Most abnormal test results turn out not to be cancer. False-positives are more common in younger women, women who have had previous breast biopsies, women with a family history of breast cancer, and women who take hormones, such as estrogen and progesterone. The skill of the doctor also can affect the chance of a false-positive result.

Mammograms expose the breast to radiation.

Being exposed to radiation is a risk factor for breast cancer. The risk of developing breast cancer from radiation exposure, such as screening mammograms or x-rays, is greater with higher doses of radiation and in younger women. For women older than 40 years, the benefits of an annual screening mammogram may be greater than the risks from radiation exposure.