Mammography Essentials
What is mammography?
Mammography is the radiological technique of imaging the breast. A mammogram is the X-ray film, or picture, of the tissue, fat, milk ducts, and other components of the breast. Mammography is the only tool currently available for detecting early cancers. When mammography is used by healthy women on a regular basis to monitor the health of the breast, it is called "routine mammography" or "screening mammography." When used to investigate unusual symptoms or as a follow-up to a clinical breast exam during which a mass was felt, the procedure is called "diagnostic mammography."
What are the benefits of routine mammography?
Routine mammography can detect a breast cancer when it is small and, sometimes, at an earlier stage. Earlier cancers respond better to treatment, and both the short-term and long-term death rates from breast cancer are generally lower for screening-detected cancers. The amount of benefit an individual woman obtains from routine mammograms depends on her initial risk of dying from breast cancer.
What are the risks of routine mammography?
The risks of routine mammography (or any other type of screening or medical intervention) are more complex and more difficult to measure than the benefits. The risks include:
False negative results: A screening mammogram that does not detect an existing cancer is termed a "false negative." This false negative result often gives the mistaken reassurance that breast cancer is not present.
False positive results: Most abnormalities on mammograms result from benign breast problems or testing errors. However, all abnormal results involve additional testing, expense, anxiety, and the possibility of a biopsy or other surgery. Approximately 10% of all screening mammograms in the United States yield a false positive result.
Over-diagnosis and over-treatment of low-risk cancers: Some cancers grow so slowly that they can be treated successfully even if they are identified months or years later. Some of the very small cancers (and precancerous conditions) that are identified by screening will never produce a medical problem during the woman's lifetime.
Exposure to radiation: Modern mammography uses a very low dose of radiation. This amount of radiation is estimated to cause one additional death from breast cancer per 10,000 women. Younger women, or those who have a mutation on the BRCA1 or 2 genes, are believed to be at greater risk of radiation-induced cancers from screening mammography.
At what age should I begin getting regular mammograms?
The American Cancer Society, the National Cancer Institute, the U.S. Preventive Services Task Force, and the American College of Physicians all recommend that women aged 50-69 get routine mammograms. No organization recommends routine mammograms for women who are under the age of 40. The four groups have differing opinions as to whether a woman should get a mammogram every year or every other year.
Conclusions about the effectiveness of routine mammograms for women in their forties are more controversial. All of the randomized trials agree that there is no difference in the death rates from breast cancer between screened and unscreened premenopausal women for the first 10 years after screening is started. Three regional studies found a trend towards reduced mortality (15–18% fewer deaths) that began 12–14 years after the beginning of the studies. In the Health Insurance Plan (New York) and Edinburgh studies, the investigators directly measured the long-term death rates of cancers diagnosed at ages below 50 and found no effect of routine screening. In the Swedish trials, a mathematical model estimated that mammograms obtained before age 50 might have a delayed effect on deaths from breast cancer and could therefore reduce later mortality from breast cancer by three percent.
All original studies, and all reviews of the original studies, agree that if routine mammography at ages below 50 is effective at all, the effect is a small one. A large effect would have been spotted, given over 2 million woman-years of observation; a very small effect might have escaped notice. Some groups and professional organizations prefer to recommend routine mammography beginning at age 40, just in case there are some screening situations or some subgroups of women for whom a small benefit may exist.
Two ongoing randomized trials of mammography screening for women under age 50, the UK Age Trial and EUROTRIAL, should give us more insight within a few years. Although the results of these trials are not likely to differ greatly from the results of the first eight trials in four countries, they may be able to identify particular subgroups of premenopausal women who might benefit from routine screening.
