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Annual screening does not reduce breast cancer deaths: U of T study

Researchers found 22 per cent of women whose invasive cancer was detected by mammography were over-diagnosed and received unnecessary treatment (photo by Rhoda Baer via the National Cancer Institute)

Annual mammograms of women between 40 and 59 do not reduce breast cancer death rates compared to regular physical examination or usual care, concludes a 25-year study from the University of Toronto’s Dalla Lana School of Public Health

The study, published on February 11 in the British Medical Journal, found that annual mammograms often pick up a lot of small, harmless cancers that will never cause symptoms or death in a patient's lifetime.

“The use of mammography to screen for breast cancer ought to be rethought,” said Anthony Miller, professor emeritus in the Dalla Lana School of Public Health.

While recognizing that these results may not be generalizable to all countries, Miller said:

“In technically advanced countries, our results question the rationale for mammography screening which should therefore be urgently reassessed by policy makers.”

The study compared breast cancer incidence and mortality in more than 89,000 women aged 40-59 who did or did not undergo mammography screening.

During the 25-year study period, the number of women in the mammography arm who developed breast cancer was similar to the number of breast cancers seen in women who did not have annual screening. The number of women who died of the disease was also similar.

“In addition to not changing the number of women who died from breast cancer, 22 per cent of the women who had an invasive breast cancer detected by screening actually would never have been bothered by their breast cancer. They were over-diagnosed and received unnecessary treatment,” said Professor Cornelia Baines of the Dalla Lana School of Public Health in an interview with CTV News.

“There’s no justification for spending in North America billions of dollars on breast screening,” said Baines.

Baines and Miller agree that education, early diagnosis and excellent clinical care should continue, but their research shows that annual mammography “does not result in a reduction in breast cancer specific mortality for women aged 40-59 beyond that of physical examination alone or usual care in the community.”

Professor Steven Narod, senior scientist at Women’s College Research Institute and Associate Professor Teresa To, senior scientist in Child Health Evaluative Services at The Hospital for Sick Children also collaborated on the study.

Nicole Bodnar is a writer with the Dalla Lana School of Public Health at the University of Toronto.