One expert questions methodology
One of the experts who was approached by Medscape Medical News to comment on the new study, Philippe Autier, MD, MPH, PhD, University of Strathclyde Institute of Global Public Health at the International Prevention Research Institute, Dardilly, France, questioned the methodology of the study. “This method is incorrect simply because women attending screening are different from women not attending screening,” he said. “The former are more health aware and have healthier behaviors than the latter, and this is a well-known fact and supported by the literature.”
Autier emphasized that it is practically impossible to control for that bias, which is known as confounding by indication.
“The statistical methods used for attenuating the so-called self-selection are very approximate and based on unverified assumptions,” he said. “For this reason, the Handbook on Breast Cancer Screening produced by the International Agency for Research on Cancer [IARC] clearly stated that ‘observational studies based on individual screening history, no matter how well designed and conducted, should not be regarded as providing evidence for an effect of screening,’ and the methodology in this paper has never been recommended by the IARC.”
A better way of conducting this type of study would have been to show the incidence trends of advanced-stage breast cancer in Sweden for the entire female population aged 40 years and older, he asserts. Autier used that methodology in his own study in the Netherlands, as previously reported by Medscape Medical News. That study found that in the Netherlands, screening mammography over a period of 24 years among women aged 50 to 74 years had little effect on reducing rates of advanced breast cancer or mortality from the disease.
Experts applaud the new findings
Three of the experts who were approached by Medscape Medical News to comment on the new findings applauded the efforts of Duffy and colleagues in providing evidence that mammography can reduce breast cancer–related mortality.
Marie Quinn, MD, director of diagnostic radiology at Roswell Park Comprehensive Cancer Center, Buffalo, New York, said this study adds to the growing body of scientific evidence that confirms that women who undergo regular screening mammography significantly reduce their risk of dying from breast cancer.
“Women who underwent regular screening also had a 25% reduction in the incidence of advanced-stage breast cancer,” she said. “This is important, because breast cancers are less fatal and often require less treatment when picked up at an earlier stage. We know the risk reduction benefit detected in this well-designed study can be attributed to screening mammography and not advances in cancer treatment, due to the long-term follow-up and outcome of cancer death within 10 years.”
The findings from this study support the guidelines recommending routine screening mammography in the United States, Quinn continued, but she pointed out that some aspects of screening (e.g., the age at which to begin screening and how often to screen) can vary. “This can be confusing for patients and providers,” she said. “Overall, research has shown us that women who undergo regular screening mammograms reduce their risk of dying from breast cancer. For women of average risk, the benefit of mammography is maximized with annual screening beginning at age 40,” she said.
Jay A. Baker, MD, FACR, FSBI, chief of the Division of Breast Imaging at Duke University Medical Center, Durham, North Carolina, emphasized that this is yet another study that confirms that the improvement in breast cancer mortality is not the result of improved treatments alone, as some have speculated. “Others have tried to model the benefit of screening vs treatment, but this study is a more direct measurement,” he said. “This conclusion is important for both patients and physicians to hear.”
Although the study strongly supports regular screening for all women, it does not specifically address which set of screening guidelines is optimal, Baker commented. “Fortunately, even though some organizations in the US curiously suggest a delayed start to screening, all organizations and professional societies agree that the most lives and the most years of life are saved by yearly screening beginning at age 40,” he added. “This new study tells us that new treatments alone aren’t enough and confirms that screening saves at least one-third more lives.”
Another expert, Bonnie N. Joe, MD, PhD, professor in residence and chief of breast imaging in the Department of Radiology and Biomedical Imaging at the University of California, San Francisco, agreed that the study shows the mortality benefits of regular screening mammography. “Notably, these benefits were related to participation in mammography screening and independent of any advances in treatment,” she said, “And these findings in this study support regular screening mammography to reduce advanced-stage breast cancers and to reduce a woman’s risk of dying from breast cancer.”
Joe noted that overall, this was a “well-done, large-scale screening study with long-term outcomes and should be applicable to other populations. In the US, we know that peak cancer incidence is in the 40s for minority women, and the results of this study support regular screening starting at 40.”
The study was supported by the American Cancer Society through a gift from the Longaberger Company’s Horizon of Hope Campaign. Additional financial support was provided by Brostcancerförbundet, Sweden. Duffy, Autier, Quinn, Joe, and Baker have disclosed no relevant financial relationships. One coauthor of the study has disclosed relationships with industry, as noted in the original article.
This article first appeared on Medscape.com.