There’s a new study making news today that concludes that breast cancer screening has not played a direct part in the reductions in breast cancer mortality in recent years in countries where screening has been implemented. For the study, published on bmj.com, lead author Phillipe Autier and colleagues compared breast cancer mortality trends in three pairs of adjacent countries in which one country introduced mammography screening some years earlier than the other (Sweden vs. Norway; Northern Ireland vs. Republic of Ireland; and Belgium vs. Netherlands). Comparing breast cancer death rates between 1989-2006, the authors observed similar trends in the reduction of breast cancer deaths in each country pair. They conclude that mortality trends are more likely to be influenced by improvements in therapy than the effect of mammography screening.
So what are we to make of this? Because even with all the debate about when mammography should start, experts agree that mammography reduces mortality. Nearly lost in the controversy over its new guidelines was the fact that the United States Preventive Services Task Force (USPSTF) in its headline making 2009 revision said “Mammography screening reduces breast cancer mortality by 15% for women aged 39 to 49 years.”
Here’s what Otis Brawley, M.D., chief medical officer, had to say about the new study.
“Measuring the impact of screening at the population level is challenging. So while it would make sense that there should be bigger drops in mortality in those countries where mammography was introduced first, there are several plausible reasons why this analysis failed to show that difference.
“First, the study does not measure how many women were actually screened. Second, just because two countries seem to share similar geography, doesn’t mean that their breast cancer mortality trends are easily compared. For example, Sweden had about 10% greater breast cancer incidence than Norway during the study period. Higher incidence would clearly influence mortality rates over time. Also, while Sweden began introducing screening in 1986, not all counties introduced it in that year, and of course, not all women received a mammogram in 1986. It takes time to invite the population to screening, and full implementation didn’t occur until 1992-1993. Third, and most important, many of the deaths attributable to breast cancer during the time period were diagnosed long before screening was introduced. In other words, there was not enough time to measure a population wide effect in this study. Finally, we don’t know how effectively mammography is functioning in the countries in these comparisons. The effectiveness of mammography on a population-wide basis will be influenced by how many women get screened and the accuracy of the screening.
“Despite those important limitations, this study does demonstrate that over time, improvements in therapy and breast awareness have contributed to a reduction in breast cancer deaths. Indeed, in some countries where mammography is not available, hospitals have measured a steady decline in the size of breast tumors that women detect themselves. A heightened awareness of breast symptoms and the importance of seeking care right away can contribute to breast cancer being treated earlier, resulting in improved prognosis.
“The American Cancer Society continues to advise women age forty and older to get a high quality mammogram and clinical breast examination on a regular basis. We believe mammography is important part of a woman’s preventive health care plan. The American Cancer Society also emphasizes the value of breast awareness, much of which stems from early detection efforts. Breast awareness is the concept that women should know how their breasts normally look and feel, be alert for changes, and when there are changes, seek expert help. Mammography is not perfect. It will not detect all breast cancers, and not all women are at an age when mammography is recommended. That’s why a heightened sense of awareness is an important complement to regular mammography screening.”