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, scientist Martin Yaffee comments on why he rejects most of the new breast-cancer screening guidelines. Click here to read Dr. Cornelia Baines's comments on why she supports them.
When I began my work as a breast cancer researcher in 1978, my goal was to improve mammography to save women's lives. I helped develop digital mammography and tested it in a clinical trial with 50,000 women in the U.S. and Canada. In 2005 in The New England Journal of Medicine, we reported that for women under 50 and, especially for those with dense breasts, digital was significantly more accurate than film in finding breast cancer. Our current goal is to develop a better way than mammography to detect breast cancer. There are some promising ideas but we're not there yet. Until that happens mammography is the best proven tool for saving lives. I have been carefully reading the science related to breast cancer detection for over 30 years and based on the evidence I must reject most of the Task Force recommendations on breast cancer screening.
One sixth of breast cancer deaths and 40 per cent of years of life lost come from cancer that arises from women in their 40s. All the fuss that's been in the news is not because earlier detection of breast cancer with screening doesn't save lives. It does. Even the Task Force, despite not recommending screening for women in their 40s, agrees it reduces deaths by 15 per cent. And that's with antiquated 1980s mammography; with modern technology it's more like 24 per cent. By the way, that study was from before digital mammography was introduced – we should be able to do better for women under 50 now. Most oncologists agree that this benefit comes from being able to use improved therapies on less advanced cancers found through screening. It's the combination of these two factors that provides the benefit.
There are additional benefits to earlier detection. When cancers are less advanced, chemotherapy may not be necessary – reducing harm to the patient and costs for the health care system. The female doctors I work with know this and many of them (women at average risk for breast cancer), some who are leading breast oncologists who treat women with breast cancer every day, have gone for screening since they were in their 40s. But currently, some provinces like Ontario where we live, won't allow women in that age group into their screening program. And if they heed the Task Force, they never will.
We all agree that mammography isn't perfect – it misses some cancers, finds some that aren't potential killers and finds others too late. At a given time, most women don't have breast cancer. We have to screen a lot of women to find the few who do and potentially save their lives. These are shortcomings of screening, not harms. The Task Force has used language that distorts the facts. An example is "false positives", which they identify as a major harm. Consider this: for 93 per cent of women screened, a single 4-image mammography exam allows the doctor to determine that she doesn't have breast cancer. For the other 7 per cent, some additional non-invasive imaging views are required. Is that an unacceptable harm? But that 7 per cent is what the Task Force calls "false positives" and considers to be harmful enough to outbalance the potential to save lives.
To continue with the numbers, within that 7 per cent about .8 per cent would receive a needle biopsy and .3 per cent would be found to have breast cancer. So, yes, I would agree that the half per cent ( .8 minus .3) of women screened who get a biopsy and don't have cancer, have endured some harm. A modern biopsy is not surgery. It is done as an outpatient procedure with a needle and is certainly not pleasant, but the women who get to that stage have a 40 per cent chance of having cancer. And, I would think that few people would question the value of the biopsy at that point.
Why has the Task Force grossly undervalued the benefits of screening while overstating the harms? Because their method of analysis caused them to include studies that used outdated imaging technology, while they refused to consider some well-conducted studies with modern equipment. I can only suppose that they inflated the harms due to their limited understanding of medical imaging and breast cancer treatment and their very restricted consultation with people knowledgeable in these areas. Unfortunately, Globe and Mail columnist Margaret Wente got it wrong as well by misinterpreting some of the numbers they used in her article and this has only increased the confusion. While Globe and Mail columnist André Picard doesn't like the pink ribbon marketing of screening, screening does save lives and he misinterpreted the cost effectiveness of screening in his article.
In Canada, each year the lives of about 200 women could be saved through screening in their 40s. And these are women in the prime of life, often working and raising their children. When we consider the years of life that could be saved for these women (as the researchers who assembled the evidence for the U.S. Task Force did) the benefit becomes even stronger for the women in this group. Both The U.S. and Canadian Task Forces chose to ignore this in formulating their recommendations. Over all age groups, the deaths of about 1,300 women would be prevented each year by screening. This is not just my opinion – this comes from peer-reviewed published science.
The Task Force is correct that clinical breast examination by a doctor or nurse or self examination don't do much to reduce mortality if women are already receiving mammography screening. But for women in their 40s their recommendation leaves them with nothing, effectively telling them to wait until a cancer becomes advanced before seeking attention. Based on the science, this is insane.
Research going on now will provide more accurate screening methods and ways to fingerprint cancers once they are found (but first they must be found!) so we can treat the deadliest ones aggressively while sparing chemotherapy for those cancers that are highly unlikely to spread and kill. In the meantime, mammography screening works and saves lives. Women and their doctors who advise them have the right to accurate and up-to-date information about benefits and limitations. (The Task Force has failed at this). Only then can women make an informed decision to be screened or not.
Martin Yaffe, PhD, senior scientist and Tory Chair in cancer research at Sunnybrook Research Institute and professor at the University of Toronto.