1. What is the best method of detecting breast cancer as early as possible?

   Depending on a woman’s age, getting high-quality screening mammograms on a regular basis is the most effective way to detect breast cancer early. Available studies do not provide enough information to know whether breast examination by a trained medical professional (called a clinical breast exam) adds benefit beyond mammography, or whether digital mammography or magnetic resonance imaging (MRI) are any better than regular film mammography for most women.

2. What are the benefits of screening mammograms?

   Research shows that screening mammography helps reduce the number of deaths from breast cancer among women ages 50 to 74 by about 17 percent. Starting screening at age 40 instead of age 50 helps reduce breast cancer mortality by an additional three percent. No benefit has been shown for regular screening mammography or baseline screening mammograms (mammograms used for comparison) among women under age 40 or over age 74.

3. What are the potential harms of screening mammograms?

   Similar to other medical tests and procedures, screening mammography has both benefits and potential harms. The potential harms of mammography include the following:

   • Finding cancer through screening does not always mean saving lives—Even though mammograms can detect malignant tumors that cannot be felt, treating a small tumor does not always mean that a woman’s life will be saved. A fast-growing or aggressive cancer may have already spread to other parts of the body before it is detected. In addition, detecting breast cancer early with mammography may not help a woman who is suffering from other, more life-threatening health conditions.
     
     
   • False-negative results—Mammograms can miss up to 20 percent of breast cancers that are present at the time of screening. The main cause of false-negative results is high breast density. Breasts are composed of dense tissue (glandular tissue and connective tissue, together known as fibroglandular tissue) and fatty tissue. Fatty tissue appears dark on a mammogram, whereas both dense tissue and tumors appear as white areas. Because of the similar density of fibroglandular tissue and tumors, tumors can be harder to detect in women with denser breasts. False-negative results occur more often among younger women than among older women because younger women are more likely to have dense breasts. As a woman ages, her breasts usually become more fatty, and false-negative results become less likely. False-negative results can lead to delays in treatment and a false sense of security for affected women. 
     
     
   • False-positive results—False-positive results occur when radiologists decide that mammograms are abnormal but no cancer is actually present. All abnormal mammograms should be followed up with additional testing (diagnostic mammograms, ultrasound, and/or biopsy) to determine whether cancer is present. False-positive results are more common in younger women, women who have had previous breast biopsies, women with a family history of breast cancer, and women who are taking estrogen (for example, menopausal hormone therapy). False-positive results can lead to anxiety and other forms of psychological distress in affected women. The additional testing required to rule out cancer can also be costly and time consuming and can cause physical discomfort.
     
     
   • Overdiagnosis and overtreatment—In addition to finding tumors that need to be treated, screening mammograms can identify tumors that will never cause symptoms or threaten a woman’s life, leading to the “overdiagnosis” of breast cancer. Treatment of these non-life-threatening tumors is not needed, leading to “overtreatment,” and exposes women to possible adverse effects associated with cancer therapy. Because doctors cannot currently distinguish breast tumors that need to be treated from those that do not, they are all treated.
     
     
   • Radiation exposure—Mammograms require very small doses of radiation. The risk of harm from this radiation exposure is slight, but repeated x-rays have the potential to cause cancer. The benefits, however, nearly always outweigh the risk.
   
   
4. When should women start getting mammograms and how often should they have them?

   The National Cancer Institute (NCI) recommends the following:

   • Women age 40 and older should have mammograms every 1 to 2 years.
   • Women who are at higher than average risk of breast cancer should talk with their health care providers about whether to have mammograms before age 40 and how often to have them.

   Other U.S. organizations have also made recommendations for screening mammography. The following table summarizes the recommendations of major U.S. organizations, including NCI.   

   Mammography Screening Recommendations for Women at Average Risk of Breast Cancer
   Organization	Recommendation
   National Cancer Institute (NCI)	Beginning at age 40, every 1-2 years
   U.S. Preventive Services Task Force (USPSTF)	Before age 50, the decision about when to start screening every 2 years should be an individual one, taking into account a woman’s risk factors and values regarding the specific benefits and harms of mammography Ages 50-74, every 2 years
   American Cancer Society (ACS)	Beginning at age 40, every year
   American College of Obstetrics and Gynecology (ACOG)	Ages 40-49, every 1-2 years Ages 50 and older, every year

For More Information:

• Call NCI’s Cancer Information Service at 1–800–4–CANCER (1–800–422–6237)
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