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New studies split over benefits of breast-cancer screening

In a study published last month in the British Medical Journal, women were told that breast cancer screening programs seem to have no effect on mortality. A week later, a study published in the Journal of Medical Screening concluded that regular mammograms are beneficial and save two lives for every one woman who receives unnecessary treatment.

It's a contradictory message that perfectly highlights the dichotomy taking hold in the breast-cancer community. It also sends a sober message about how this increasingly political and emotional debate risks leading to confusion and fear.

Proponents of screening programs say they save lives by detecting cancer early. They point to the fact breast cancer mortality rates have been falling steadily in recent decades, a trend they say is due in part to improved access to screening.

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But a growing number of critics say it's time to completely rethink routine mammograms, because evidence shows they may not be effective and can actually lead to over-diagnosis or unnecessary treatment. While agreeing that deaths from breast cancer are falling, they credit improved treatment and increased public awareness. They say their message isn't being heard, however, because parties with vested interests in maintaining screening programs are drowning them out.

"People don't like having their beliefs threatened," said Cornelia Baines, professor emerita in the department of public health sciences at the University of Toronto, who led a 2002 study that found regular mammograms didn't affect mortality rates for Canadian women in their 40s.

It's a significant issue, because routine mammograms put women at risk of being misdiagnosed and having to have a biopsy unnecessarily. Along with the anxiety of a false positive result, they may also undergo unnecessary exposure to radiation.

A discussion over the merits of routine breast cancer screening programs has been heating up for years. But it reached a boiling point in November, when U.S. health officials recommended that women undergo routine screening starting at age 50 instead of 40. In Canada, current recommendations already call for women to be screened starting at age 50, although some provinces allow routine screening for women who are 40.

Those in favour of routine screening programs point to research, such as last month's study in the Journal of Medical Screening, which found mammograms save two lives for every woman who goes through treatment unnecessarily. Stephen Duffy, professor of cancer screening at Queen Mary University of London and Cancer Research UK, led the study, which was carried out in Sweden. He said it shows that, while not perfect, screening saves lives.

"Not just from this study but from a large body of evidence, it's clear to me screening does prevent deaths from breast cancer," Prof. Duffy said in a telephone interview.

He added that a majority of studies that have found problems with screening programs often focus on time periods that are too short and therefore miss some cancers that would have been detected later in a woman's life.

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But another study in the British Medical Journal, which followed two groups of Danish women in various age groups who either had universal access to routine screening or not. There was little difference in mortality rates between the two groups after 10 years.

Groups such as the Canadian Cancer Society and the Canadian Breast Cancer Network criticized the study and said Canadian policy should not be changed.

"Screening by mammogram is the most important test that a woman can undergo to increase her chance of survival," said Cathy Ammendolea, president of the Breast Cancer Network, in a statement. Despite several requests, the group didn't provide a spokesperson for an interview.

Dr. Baines said those kinds of messages are precisely why it's so difficult to have a rational discussion over the effectiveness of mammograms. The belief that screening is beneficial has become so entrenched in the breast cancer community that people don't want to hear that conventional wisdom may be flawed. As a result, the only message the public hears is that screening works and women need it.

"Women are frightened and so you can understand if there's a threat of withdrawal of the agent that's going to save them, they're going to be upset," she said.

However, she doesn't expect the debate will ever go away, or that Canadians will see any significant policy shift.

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"I don't believe this controversy will ever be over until we have a blood test for breast cancer," Dr. Baines said.

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About the Author

Carly Weeks has been a journalist with The Globe and Mail since 2007.  She has reported on everything from federal politics to the high levels of sodium in the Canadian diet. More

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