Screening Mammography

Screening mammography – is it harmful or helpful?

Hard to think that it could be harmful when so many women go through the procedure.

In Medicine Hat, 1989 was the first full year of mammography when 1046 mammograms were done at the Medicine Hat Regional Hospital (MHRH). These were mostly for screening (women with no palpable breast lump or symptoms) and some were diagnostic (women with breast lumps or with symptoms).

In the last four years, MHRH has transferred mammography services to the private clinic (Blair Stubbs and Associates Radiology Inc.). In 2001, Blair Stubbs did total of 5229 mammograms. In 2002, they did 7454 mammograms (screening 5857, diagnostic 1597).

An article in the New England Journal of Medicine (NEJM) says that 71 per cent of women in the United States who were 40 years of age or older have undergone mammography during the previous two years – an increase from 54 per cent in 1989.

Good news is that since 1973, mortality from breast cancer has been decreasing steadily. Is this due to treatment or due to early diagnosis from screening? Experts are not sure. Could be due to both.

For almost 20 years, there is a uniform agreement among the experts that screening mammography saves lives (20 to 35 per cent reduction in mortality) among women in their 50s and 60s, although the disagreement persisted about the usefulness of screening mammography in other age groups, says the NEJM article.

For many years, there has been controversy over the use of screening mammography for women in their 40s. Analysis of multiple studies show that screening in this age group decreased 15-year mortality from breast cancer by about 20 percent.

What about older women? Studies in the Netherlands found that screening women between 65 and 74 years of age led to a 55 percent decrease in mortality from breast cancer, says the NEJM article.

Sounds wonderful. But are there any risks associated with mammograms?

False positive mammograms and over diagnosis can be harmful. Here are the numbers:

-An average of 11 percent of screening mammograms is read as abnormal and necessitates further diagnostic evaluation.

-Breast cancer is found in about three percent of women with an abnormal mammogram (representing 0.3 percent of all mammograms).

-On average, a woman has about a 10.7 percent chance of a false positive result with each mammogram.

-After 10 mammograms, about half of women will have had a false positive result, which will have led to a needle biopsy or an open biopsy in 19 percent of cases.

-False positive mammograms increase patients’ anxiety.

-12 months after a false positive mammogram, women initiated more health care visits for both breast-related and non–breast-related problems.

Some women find mammography painful, there is a small radiation exposure, and false negative interpretations are possible in about 15 per cent of mammograms.

Like any screening and diagnostic test, mammography is not a perfect science. It should be interpreted with care in combination with clinical examination, needle biopsy, and any other tests which may become necessary to come to a diagnosis.

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