Moira Stilwell does not enjoy having mammography tests that could detect cancer in her breasts. "They're physically uncomfortable," she says, "and every time I go through a lot of 'what if?' worrying about maybe finding out I have breast cancer." Stilwell, 46, a physician herself and co-director of the breast health program at the British Columbia Women's Hospital in Vancouver, has never had breast cancer. Yet once a year, she sets aside her inclinations and allows her breasts to be flattened between plastic plates and exposed to low-dose X-rays. Like many doctors, Stilwell believes mammography combined with physical examination is the best way to detect early evidence of breast cancer, a disease that this year will kill an estimated 5,500 Canadian women. Breast cancer mortality rates in Canada and some other countries have been declining - and many experts think increased use of mammography is one of the reasons. "I urge women to have mammograms," says Stilwell. "I can't think of any good reason why most women shouldn't."
Stilwell maintains that opinion despite a major Canadian study published last week that cast doubt on the value of mammograms and endorsed physical breast examinations as an alternative. In a follow-up report on a breast cancer study that began 20 years ago, researchers concluded that for women in their 50s - the group most at risk of breast cancer - mortality rates were the same regardless of whether they had regular mammograms and physical breast examinations or simply had their breasts examined by doctors and nurses. The finding generated widespread media coverage, including a wildly misleading front-page headline in the National Post that declared: "Mammograms pointless."
That was not the message cancer specialists want women to hear. "We don't want women to think that just because a doctor runs his hands over her breasts for a minute or two she doesn't need a mammogram," says Dr. Daniel Rayson, a Halifax oncologist. The most that should be drawn from the study, says Dr. Barbara Whylie, the Canadian Cancer Society's medical affairs director, is that for women who don't have access to mammography or find the tests too painful, "regular physical examinations by qualified personnel may be an option."
Almost from the start, the ambitious Canadian National Breast Screening Study has generated criticism and controversy. Launched in 1980, the project involved nearly 40,000 women divided into two groups, one for screening by mammograms and physical examinations and the other by physical exams alone, at 15 centres. A preliminary follow-up study was widely challenged in 1992 when it found no significant differences in mortality rates between the groups. The latest report reached the same conclusion: 12 years after the study period ended, 107 of the women who had mammograms and physical examinations, and 105 of those who only had physical examinations, had died of breast cancer.
The study did find that mammograms were better than physical examinations for early detection of small non-invasive cancers, though that did not appear to affect long-term mortality rates. "We're not saying that mammograms aren't useful," says Dr. Anthony Miller, the University of Toronto researcher who led the study. "The point is, women who have access to high-quality physical breast examinations can choose this option as an alternative to mammography."
Cancer specialists who vehemently challenged that conclusion cited flaws in the study that might have skewed the findings. They noted that mammography equipment available in the 1980s was less sensitive than machines currently in use. And they objected that the study used radiologists without mammography training to interpret X-rays.
To best protect themselves from breast cancer, says Whylie, women should examine their breasts often, see a physician for regular examinations as well - and have mammograms. Regardless of questions raised by the controversial new study, she adds, "Mammography is still the gold standard. The results of one study can't change that."
Maclean's October 2, 2000