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Keeping Cancer in Perspective

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Mammograms: To screen or not to screen?

The mammography debate rages on, newly fueled by results from a Canadian trial published in the Sept. 3, 2002, Annals of Internal Medicine.

The Canadian National Breast Screening Study (CNBSS) is the first trial designed specifically to assess screening mammography in women ages 40–49. In the early 1980s, the CNBSS recruited 50,430 women in this age group with no history of breast cancer. Half were assigned to receive annual mammograms; the other half, to receive “usual care,” meaning that mammograms were done only if a patient’s doctor recommended them.

After an average of 13 years, there were 105 breast cancer deaths in the mammography group and 108 in the usual care group — not statistically significant difference. The researchers concluded that mammograms are not justified for breast cancer screening in women under age 50.

Critics of the CNBSS trial said the data came from older technology, before improved imaging was available. The women who took part enrolled 20 years ago, when mammography images were less clear and radiologists weren’t as proficient at reading them.

But the American Cancer Society, the Centers for Disease Control and Prevention, and the National Cancer Institute advise women to get annual mammograms starting at age 40.

To further muddy the waters, the same issue of Annals of Internal Medicine that carried the CNBSS results published new guidelines for breast cancer screening from the U.S. Preventive Services Task Force (USPSTF). The USPSTF is a panel of health experts that analyzes published research and makes suggestions about preventive health care.

The group recommends having a mammogram every one to two years, starting at age 40. The authors assert that there is no convincing evidence to support the theory that starting annual screening at age 40 exposes women to undue harm, with minimal chances of finding cancer.

On the other hand, if mammograms can find breast cancer, why not start at age 40? For one, the screening test may adversely affect some women. False-positive results (which flag a problem when none exists) can lead to anxiety and further testing.

In defense of its recommendations, however, the USPSTF says that anxiety usually disintegrates after cancer is ruled out. And even when it doesn’t go away, anxiety doesn’t seem to discourage women from continuing their screening regimen.

If you have a family history of breast cancer or other risk factors, it makes sense to start mammograms at age 40 (perhaps earlier, depending upon your level of risk). For everyone else, a discussion with your doctor is the most sensible first step. If she or he feels annual mammograms are unnecessary for you, and you’re comfortable with the decision, waiting until you’re 50 should be fine.

November 2002 Update

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