Last week, the Canadian Task Force on Preventive Health Care released the new screening guidelines for women with an average risk of developing breast cancer. The guidelines recommend that women under 50 do not have screening mammograms. Click here to read our coverage of the guidelines.
Here, Dr. Cornelia Baines comments on why she supports the new breast-cancer screening guidelines. Click to read scientist Martin Yaffe's comments on why he does not.
According to the Canadian Task Force on Preventive Health Care, which has released new guidelines for breast cancer screening, 2,100 women at average risk of breast cancer, age 40 to 49, would have to be screened every two years for 11 years so that one woman (0.005 per cent) will escape breast cancer death. However, to achieve that benefit, 700 women will experience a false-positive mammogram requiring further imaging with 75 proceeding to biopsy, all to confirm that they do not have breast cancer. Women with screen-detected cancer face a 20 per cent increased risk of mastectomy. Most disturbing, at least 10 women will be unnecessarily treated for breast cancer and bear the burden of over-diagnosis. I conclude that screening is not highly advantageous for such women. The news of the new guidelines have "confused women and doctors," according to media reports.
Clearly many people have not been listening to the full screening story. Since 1992, objective expert panels (four in the U.S., two in Canada and three in Europe) have released similar evidence-based messages. Initially it was found the benefit for women 40 to 49 was questionable and small. Recently, observational studies are persuasively demonstrating that declines in breast cancer deaths (up to 37 per cent in unscreened women age 40 to 49!) have occurred in the absence of screening programs. This decline is likely due to increased awareness, tamoxifen and adjuvant chemotherapy – three elements absent when most screening trials were conducted. Thus there was more opportunity for screening to be effective 30 years ago than is the case now.
Despite this overwhelming evidence why is it that many women still have faith in mammography and why are some members of the medical community challenging the guidelines?
Expert guidelines and the good news about death rates have not been widely reported or accepted – media reports focus on survivors and how mammography saves lives. Women, desperately afraid of breast cancer, rely on mammography, which may give some of them a sense of control over their health. Furthermore, some of the experts who challenge the new guidelines are in a conflict of interest - their livelihood and prestige depend on screening.
In an opinion piece published in 2010 in the New England Journal of Medicine, two U.S. scholars, K.H. Quanstrum and R.A. Hayward, said it was time to stop "loud voices" – those in the imaging industry – from determining public policy surrounding breast cancer screening. Also last year, two American radiologists, Leonard Hall and F.M. Hall, disclosed in the journal Radiology how General Electric HealthCare and Siemens (both of which make imaging equipment and donate to the American College of Radiology) together with the College led the pro-screening lobby that was determined to undermine the U.S. Preventive Services 2009 guidelines for breast screening, compatible with the current Canadian guidelines. (Canada had already embraced the idea that screening women under the age of 50 may do more harm than good.)
Last week a letter in The Lancet, a British-based medical journal, got a lot of media attention. Those who signed the letter claimed there is "an active anti-screening campaign orchestrated in part by members of the Nordic Cochrane Centre." (The Centre, an independent body that evaluates medical evidence, recently published a study that concluded that women undergoing mammography should be "fully informed of both the benefits and harms" of screening.) The letter went on to say screening guidelines produced by the Centre "are scientifically unsound." They ended their letter with this statement: "We declare that we have no conflicts of interest.
However, the majority of those who signed the letter are involved in screening in one way or another. For instance, one of the signers is a radiologist and offers mammography courses to the medical community in both North America and Europe. He has been doing this since the mid-1980s. You can attend his course in Scottsdale Arizona for a mere $1,800 (U.S.), registration limited to 100. He promotes his business online.
To sum up, a number of reasons explain why some do not like the guidelines. Women are afraid of breast cancer and have faith in mammography. Doctors fear litigation if they fail to recommend screening for a woman who subsequently develops breast cancer. And even when doctors are informed about expert guidelines, many tend to ignore them. Politicians, especially in the U.S. are loathe to provoke the ladies with pink ribbons. Last but not least are very real but usually ignored conflicts of interest.
Dr. Cornelia Baines, professor emerita, Dalla Lana School of Public Health at the University of Toronto.