NBCC has taken the position for many years that the benefits of screening mammography in reducing mortality are modest and that there are harms associated with screening, based on randomized clinical trial data. No individual woman can be assured that screening mammography will be effective for her, and from a public health perspective, the harms and public health costs of screening mammography may outweigh the modest benefits of the intervention. Last week, Dr. H. Gilbert Welch and Dr.Archie Bleyer published a study looking at over three decades of data, providing strong observational evidence that this is indeed the case.
The study, published in the NEJM, looked at the impact of mammography screening on breast-cancer incidence between 1976 and 2008 in US women over 40. The authors examined the change in incidence of early-stage and late-stage breast cancer after the introduction of wide-spread screening in the mid-1980s. They found that while the incidence of early-stage (DCIS and breast cancer localized to the breast only) increased significantly, the incidence of late-stage (regional and metastatic breast cancer) decreased only slightly.
The incidence of metastatic breast cancer, the number we most need to change with screening, had not changed at all over the three decades. Dr. Welch and Dr. Bleyer estimate that over one million women have been over-diagnosed as a result of mammography screening, and have undergone treatments involving surgery, radiation, hormones, and chemotherapy for abnormalities that otherwise would not have caused illness. Dr. Welch explains the study and results in a brief YouTube presentation for advocates and the public. Watch it here.
Following publication of the study, Dr. David Newman wrote in the NYTimesWell blog, “It is affirming to see this newest study. But it raises an awkward question: why would a major medical journal publish an observational study about the effects of screening mammography years after randomized trials have answered the question? Perhaps it is because many doctors and patients continue to ignore the science on mammograms.”
It’s hard to blame the patients when the media messages are so mixed. Following directly on the heels of the NEJM study, were reports from the annual radiologists’ meeting expressing concern about decreased screening and possible “missed cancers.” They don’t acknowledge the results of randomized clinical trials and observational data showing that finding cancers and DCIS through mammography isn’t translating into significantly fewer deaths, while at the same time is causing many women to undergo treatments they would have been fine without.
NBCC continues to believe that a woman’s decision to undergo a screening mammogram must be made on an individual level, based on quality information about her specific risk factors, and her personal preferences. Women who have symptoms of breast cancer such as a lump, pain or nipple discharge should seek a diagnostic mammogram. We can only hope that the latest NEJM study will help put the issue to rest and we can move on. Ultimately, resources must be devoted to finding effective preventions and treatments for breast cancer and tools that detect breast cancer truly early.