Benefit and Harms of More and Less Frequent Mammography

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What is the problem and what is known about it so far?

A mammogram is a breast x-ray that can detect cancer before it is large enough to feel or cause symptoms. In 2009, the U.S. Preventive Services Task Force (USPSTF), a group of health experts that reviews research and makes recommendations about preventive health care, changed their mammography recommendations to advise that otherwise healthy women have mammography every 2 years beginning at age 50 years. They based this change on calculations that starting annual screening mammography later and getting it less often would cause less harm and be just as safe as starting it earlier and getting it more often. The change in recommendation was controversial because many people believe the benefits of screening mammography outweigh its harms. A study of the benefits and risks of the newer recommendations was needed.

Why did the researchers do this particular study?

To better understand the benefits and harms of less frequent mammography screening starting at age 50 years compared with age 40 years.

Who was studied?

169,456 women who had their first screening mammogram in their 40s or 50s and 4492 women diagnosed with invasive breast cancer.

How was the study done?

The researchers counted the number of times women who had mammography were called back for additional imaging that was found to be normal (false-positive recalls). They also counted how many times women were advised to get a breast biopsy but were not ultimately diagnosed with breast cancer (false-positive biopsy recommendations). They then used statistical techniques to estimate the probability that a woman would have a false-positive result over 10 years of screening if she got more or less frequent mammography starting at younger or older ages.

What did the researchers find?

Over 10 years, more than one half of women who start screening mammography every year at age 40 years could expect to be called back for additional normal imaging. About 7 of 100 of those women could expect to be advised to get a breast biopsy that would not ultimately lead to a diagnosis of breast cancer. Screening every other year reduced those probabilities. The researchers found a small increase in late-stage cancers among women who had screening every other year compared with every year.

What were the limitations of the study?

Few women had regular screening every year or every other year beginning at age 40 or 50 years. As a result, the researchers had to use statistics to estimate what would happen with more consistent patterns. The researchers could not estimate probabilities more than 10 years after starting mammography. To get reliable estimates of delayed cancer diagnoses, the researchers needed to analyze cancers in only a fraction of women who actually developed it. The cancer findings relate only to screening 1 to 3 years immediately before the diagnosis, not to patterns of screening occurring years before.

What are the implications of the study?

The findings support the recommendation that mammography every other year will reduce a woman's probability of being called back for normal imaging or a normal breast biopsy. Screening every other year may be associated with a small increase in the probability of being diagnosed with later-stage cancer.

 

Article and Author Information

• The full report is titled “Cumulative Probability of False-Positive Recall or Biopsy Recommendation After 10 Years of Screening Mammography. A Cohort Study.” It is in the 18 October 2011 issue of Annals of Internal Medicine (volume 155, pages 481-492). The authors are R.A. Hubbard, K. Kerlikowske, C.I. Flowers, B.C. Yankaskas, W. Zhu, and D.L. Miglioretti.