4 frequently asked questions about mammograms

Mammograms can cut a woman's risk of dying from breast cancer, but they aren't without controversy, especially in women under 50. Here are the answers to four of the most asked questions about this important test.

• Many medical authorities say that women should begin at age 40, but research suggests that women over 50 are most likely to benefit
• Women aged 50 to 69 who have routine mammograms reduce their risk of dying from breast cancer by 20 to 35 percent
• Mammograms offer less benefit to women under 50. Breast cancer is less common in younger women, and younger women tend to have dense breast tissue, which makes tumours more difficult to detect with mammography

Mammograms detect about 75 percent of tumours. But false positives are not uncommon, and a negative mammogram does not guarantee you're in the clear.

One study found that when women with very dense breasts have mammograms, tumours are not visible or are not detected 37 percent of the time. (By the way, roughly half of all breast cancers are detected by women themselves.) About six to 10 percent of mammograms produce false-positive results — that is, images that show what look like tumours but prove to be cysts and other harmless masses.

Mammograms are more accurate in:

• older women
• women whose breasts are mostly fat tissue, which is not dense and which X-rays can easily "see" through

Mammograms are less effective in:

• women with dense breasts and those under 50

• While the traditional mammogram is little more than an X-ray, digital mammography adds computers and special software to enhance images of breast tissue. But this technology upgrade hasn't necessarily led to better breast cancer detection
• A large study involving more than 222,000 women published in the New England Journal of Medicine found that switching from traditional mammograms to computer-aided mammograms didn't improve radiologists' ability to detect breast tumours
• Women who had computer-aided mammograms were more likely to receive false-positive test results and to require needle biopsies

Some women may benefit from having digital mammograms, however. Just keep in mind that greater accuracy may come with a higher risk of unnecessary procedures. It may be worth asking your physician about digital mammograms if:

• you have dense breasts
• you're under 50
• you haven't hit menopause yet

If you have a very high risk of breast cancer, a doctor may recommend that you undergo magnetic resonance imaging (MRI) in addition to having mammograms. You may be a candidate for an MRI if:

• you have already had breast cancer
• you have a strong family history
• you carry certain genetic markers for breast cancer
• you had chest radiation between the ages of 10 and 30
• you or a close relative have certain rare conditions that increase breast cancer risk

Studies show that MRI detects far more breast tumours in high-risk women than traditional mammograms do. However, it is also considerably less discriminating. A Dutch study of 1,909 women comparing mammograms to MRI found that the latter led to twice as many unneeded examinations and three times as many unneeded biopsies.

Mammograms are a useful screening test that can save women's lives, but they aren't perfect. Considering these frequently asked questions can help you to understand the benefits and limitations of mammograms.