Screening programs in which post-menopausal women undergo routine mammography to help detect tumours have virtually no impact on reducing breast-cancer deaths, a new study concludes.
The research, published in today's edition of the British Medical Journal, says that while breast-cancer mortality has fallen sharply over the years, there is no evidence this is due to systematic screening. Rather, the gains are likely due to better treatment and heightened awareness among women about breast health.
Dr. Karsten Jørgensen, a medical researcher at the Nordic Cochrane Centre in Copenhagen and lead author of the paper, said it is time to fundamentally rethink the current approach rather than continue to engage in wishful thinking.
"We have to start asking unpleasant questions about mammography screening," he said in an interview.
"Public institutions and large patient advocacy groups have been unwilling to admit that there are serious problems. They have tried to paint a rosy picture against mounting evidence of much smaller benefits than was originally promised and very serious harms," Dr. Jørgensen said.
Heather Chappell, director of cancer-control policy at the Canadian Cancer Society, said the new study has "very serious limitations" and it should not lead to a change in current practices.
She said it is an observational study, not a randomized clinical trial; the research did not account for movement between areas of the country where there is screening and not; and findings from Denmark are not necessarily applicable to Canada.
The CCS recommends that all women aged 50 to 69 have a clinical breast examination by a trained health-care professional at least every two years and have a screening mammogram every two years. Women aged 40 to 49 should undergo a clinical breast exam, while those over 70 should discuss their risk with a health-care professional.
"Overall, research still shows a significant benefit from screening," she said. "In Canada, we've seen a reduction in breast-cancer mortality of about 25 per cent since screening began. Treatment certainly doesn't account for all of it."
Both the researcher and the Cancer Society stressed, however, that the debate involves only screening mammography, in which women without any obvious signs of cancer are checked for presence of potential tumours. The benefits of diagnostic mammography – using X-rays to probe a lump or other abnormality – are unquestioned.
The new study included data on all Danish women recorded in the Cause of Death Register and Statistics Denmark database between 1971 and 2006. It included 17 years in which there was universal breast-cancer screening programs for women aged 55 to 74 in only two areas, Copenhagen and Funen County. In the rest of the country there is no organized screening.
Dr. Jørgensen and his team analyzed and compared data from the regions with screening and those without and found:
In the 55-to-74 age group, breast-cancer mortality declined by 1 per cent annually in areas with screening and 2 per cent a year in areas where there was no screening;
In the 35-to-54 age group, where screening is not recommended, breast-cancer mortality fell 5 per cent a year in areas with screening and 6 per cent in those without.
In the 75-and-over age group, there was no change in mortality in any area.
Breast-cancer mortality dropped steadily in the 10 years prior to screening beginning.
Dr. Cornelia Baines, professor emerita in the department of public health sciences at the University of Toronto, said the debate about the value of screening mammography has been ongoing since 1985, but it has become so emotionally and socially fraught that there can no longer be a rational discussion.
"Even though it's been done with the best of intentions, there is no doubt the benefits of screening have been hugely oversold," she said.
"This is good straightforward study but I have no doubt there will be violent reaction," Dr. Baines said.
One point on which proponents and detractors of screening agree is that, ultimately, the decision to undergo mammography is a very personal one, which entails both benefits (early detection and treatment of cancer, the peace of mind that comes from receiving a clean bill of health) and risks (the effects of radiation or false positives).
Seventy-two per cent of women aged 50 to 69 reported in 2008 that they had had a mammogram in the previous two years, according to Statistics Canada, up from 40 per cent in 1990.
In Canada, organized breast-screening programs began in 1988, and by 1998, had been established in all provinces.