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Another study questions screening mammo's value

by Loren Bonner, DOTmed News Online Editor | July 18, 2012
A new study using data from a long-running breast cancer screening program casts doubt on the life-saving benefits of screening mammography, adding to a controversial body of literature that questions the popular cancer-prevention strategy.

Sweden has offered women aged 40-69 mammography screening since 1974, a few years before it became widely available and standard practice in doctor's offices around the world.

Screening rates in the country peaked in 1997, and researchers at the International Prevention Research Institute (iPRI), an independent research institute in France, wanted to know if mortality trends were affected by increased screening for Swedish women through the decades. The findings of their research were published July 17 in the Journal of The National Cancer Institute.

Swedish mammography trials and observational studies conducted in the past have suggested that mammography leads to a reduction in breast cancer mortality. Naturally, iPRI researchers thought screening would be associated with a gradual reduction in mortality. But after evaluating data from the Swedish Board of Health and Welfare from 1960-2009, and comparing actual mortality trends with theoretical outcomes, they discovered just the opposite: breast cancer mortality rates in Swedish women started to decrease in 1972, and have continued to decline at a rate similar to that in the prescreening period.

"It seems paradoxical that the downward trends in breast cancer mortality in Sweden have evolved practically as if screening had never existed," they wrote.

But the researchers note that the study-being observational-didn't take into account the potential influences of other breast cancer risk factors, and it may have also been skewed due to the fact that it was a population-based study.

An accompanying editorial in JNCI, written by Dr. Michael Vannier of the department of radiology at the University of Chicago Medical Center, challenges the researchers approach.

"Conventional wisdom has been to use mortality as the end point for screening-program evaluation, despite the fact that diagnosis, staging, treatment, and re-treatment for recurrence take place before the end of life," he said.

Vannier added that it's been easy to use mortality records in estimating the value of medical procedures because they are readily available.

"So, without appropriate analyses, results from cancer screening trials will be distorted," he said.

Mammography, which has received strong support across the board through the years, isn't likely to disappear from mainstream medicine anytime soon. But Vannier thinks that improved diagnostic tools to evaluate abnormalities found in screenings may address some of the limits of population-based screening, such as this one.

"As our tools improve, we can begin to fully realize the promise of breast cancer screening to arrest this dread disease at its earliest stage with the least morbidity and cost," he said.

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