New research pushes back against suggestions that screening mammography may no longer be a primary factor in decreased breast cancer mortality.
Using comprehensive registries for population, screening history, breast cancer incidence and disease-specific death data for 52,438 Swedish women ages 40 to 69, the study in Cancer further substantiates the importance of screening mammography.
This research continues work that began three decades ago, says László Tabár, MD, FACR (Hon), Professor Emeritus of Radiology at the University of Uppsala School of Medicine, Former Medical Director of the Department of Mammography at Central Hospital in Falun, Sweden, and Consultant Radiologist for numerous Comprehensive Breast Centers in the U.S.
“In the early years, our focus was on evaluating the impact of invitation to mammography screening in a population-based, prospective, randomized controlled trial,” Dr. Tabár says. “The comparison was between breast cancer deaths in women invited to an organized breast cancer screening program [those taking part and those not taking part combined] versus women not invited to screening. We found significantly fewer breast cancer deaths among women invited to screening, which led to the introduction of mammography screening in many countries.”
After this initial study, Dr. Tabár says, researchers turned more directly to the question of whether regular mammography screening reduced the risk of death from breast cancer. To answer this question, Dr. Tabár’s research group focused only on women who were invited to the organized breast cancer screening program. Within that subgroup, the team continued to study the program’s impact on mortality by comparing regular participants in screening with nonparticipants.
They found that, when compared with women who did not undergo regular screening, women who received regular mammograms had a 60 percent lower risk of dying from breast cancer within 10 years after diagnosis and a 47 percent lower risk of dying from breast cancer within 20 years after diagnosis.
“Most breast cancer deaths are caused by advanced, late stage, palpable cancers that have spread to vital organs. Early detection through mammography screening dramatically reduces the incidence of advanced breast cancer in an entire population. As a result, significantly fewer women die.”
— László Tabár, MD, FACR (Hon), Professor Emeritus of Radiology at the University of Uppsala School of Medicine
The Screening Schism
Despite growing evidence from studies such as Dr. Tabár’s that screening mammography is crucial in saving lives, dubious claims against it endure.
“The arguments against mammography have changed over the years,” says Jay A. Baker, MD, FACR, FSBI, President of the Society of Breast Imaging and Professor of Radiology, Chief of the Division of Breast Imaging and Vice-Chair of Clinical Affairs at Duke University School of Medicine. “Like a Hydra, every time we discredit one theory, two more seem to pop up to replace it.”
Dr. Baker points to periodic studies over the years citing concerns about “drawbacks” of screening. An early argument was that mammography was ineffective in detecting breast cancer, he notes. However, in an era of digital breast tomosynthesis that can detect about 40 percent more breast cancers at smaller sizes than regular digital mammography, this argument is now rarely heard.
More recently, some have questioned the importance of screening mammography as more advanced therapies become available.
“In previous evaluations, we observed some benefit from advancements in therapy among women who did not participate in mammography screenings, but our data showed very clearly that modern therapies are no substitute for early detection,” says Robert A. Smith, PhD, Vice President of Cancer Screening at the American Cancer Society and a member of Dr. Tabár’s research team. “It’s our position that the argument around what is contributing more to saving lives — imaging or therapy — is really misplaced because we are steadily making improvements to each. That being said, our study showed that women who choose to participate in mammography screening benefit substantially more from existing, state-of-the-art therapies than women who do not.”
Another common concern is that screening mammography leads to overdiagnosis. While the exact prevalence of overdiagnosis cannot be tested in a clinical trial, as it would require physicians to abstain from treating cancerous lesions, some of the strongest studies available demonstrate that only 1 to 10 percent of breast cancers detected by screening mammography are overdiagnosed.
“There is also no evidence that breast cancers resolve without treatment,” says Dana H. Smetherman, MD, MPH, MBA, FACR, Chair of the American College of Radiology Breast Imaging Commission. “That means that screening less often or starting screening at a later age does not reduce the chance of overdiagnosis because the indolent cancer will simply be found on the next screening mammogram.”
Others question whether potential discomfort and anxiety related to screening mammography are worth the benefits. According to Dr. Baker, these concerns are misguided, as well.
“As someone who sees and speaks to women about their breast imaging concerns every day, I can agree that they feel anxious,” he says. “However, they aren’t anxious about screening mammograms. They are anxious that they may have breast cancer.”
Beyond the Debate
Researchers say additional enhancements to breast cancer screening are vital.
Future investigation could include studies on how to detect benign lesions in order to minimize biopsies of nonlethal growths, better identify women at high risk for breast cancer, decrease discomfort associated with screening mammography and develop more effective methods to screen dense breast tissue.
According to Dr. Smetherman, further research could foster consensus on screening recommendations among agencies and organizations such as the U.S. Preventive Services Task Force, American Cancer Society and American College of Radiology. Consistent recommendations regarding who should be screened and how often may reduce confusion, which can discourage patients from asking for regular mammograms and physicians from recommending them.
“Physicians need to talk with their patients about the benefits and limitations of mammography screening, stress its importance, and play an active role in ensuring patients get mammograms regularly,” Smith says. “There is no substitute for finding breast cancer early in its natural history.”