New evidence that annual mammograms may be overkill

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If you’re still upset about last fall’s recommendation by the U.S. Preventive Services Task Force that women begin getting mammograms to screen for breast cancer at age 50 instead of 40 – and to get them every other year instead of annually – a new study from Denmark may put you at ease.

Mammographic screening was introduced in the Danish capital of Copenhagen in 1991, and it began in Funen County (home of Hans Christian Andersen) in 1993. Between 1997 and 2006, deaths due to breast cancer fell 5% per year among women age 35 to 55 in those areas. For women between age 55 and 74 – who would benefit most from screening – the mortality rate dropped by 1% per year, and for older women there was little change.

Looks like a success for breast cancer screening right? Not so fast, the researchers said.

They also checked the corresponding mortality rates for the 80% of Danish women who didn’t participate in screening programs. In those areas, breast cancer deaths in the same decade declined 6% per year for women age 35 to 55 and by 2% per year for women age 55 to 74. (Again, there was little year-to-year change among older women.)

Those findings led the researchers to conclude that improved treatments and changes in risk factors were responsible for the reduction in breast cancer mortality, not the mammograms.

The researchers, from the University of Copenhagen and the Norwegian Institute of Public Health, also noted that the incidence of ductal carcinoma in situ – a non-invasive growth in a milk duct that sometimes progresses to breast cancer – remained essentially flat in the non-screening areas but doubled in Copenhagen and Funen County. That jibes with the concern expressed by Dr. Susan Love and others that mammograms flag many cases of DCIS that prompt invasive treatments, but wouldn’t have been harmful if left alone.

They also note that their conclusions are in line with studies from other countries. In the U.K., for example, breast cancer mortality rates declined 41% for women in their 40s (who don’t get routine mammograms) and 41% for women between age 50 and 64 (who do). In Sweden, screening was introduced after death rates started to fall and continued falling at a constant rate, suggesting that mammograms had little effect.

“We believe it is time to question whether screening has delivered the promised effect on breast cancer mortality,” the researchers wrote. Their study was published online this week in BMJ.

-- Karen Kaplan