A woman's decision to undergo mammography "should be individualized based on patients' risk profiles and preferences," concludes a systematic review of 50 years of breast cancer screening data, published in the April issue of JAMA.
How to best go about achieving that individualization is not entirely clear, but clinicians need to make an effort with the tools that are currently available, such as decision aids and risk models, suggest Lydia Pace, MD, MPH, and Nancy Keating, MD, MPH, both from Brigham and Women's Hospital in Boston, in their review.
The pair evaluated nearly 450 scientific articles from 1960 to 2014 for "evidence on the mortality benefit and chief harms of mammography screening."
After pouring over clinical trials, systematic reviews, meta-analyses, and observational studies, they conclude that the mortality benefit of mammography is "modest" and the risks of harm from screening are "significant."
This mix means that clinicians "must focus on promoting informed screening decisions," they write.
"There is a challenge for physicians to find the time to talk about this with patients," acknowledged Dr. Keating in an email toMedscape Medical News. "I do hope that the increasing availability of decision aids will make these discussions easier."
In an accompanying editorial, another pair of experts echo the main messages of the review.
"Balanced messaging is essential to help each woman make her own individual decision regarding her participation in screening mammography," write Joann Elmore, MD, MPH, from the University of Washington in Seattle, and Barnett Kramer, MD, MPH, from the National Cancer Institute in Bethesda, Maryland.
Discussions about screening "should begin with information about the woman's realistic risk of a breast cancer diagnosis," they add.
However, like Drs. Pace and Keating, the editorialists suggest there is a bit of a glitch in doing this. "The current ability to estimate individual risk is imprecise," they note.
The benefit of mammography is "less than once hoped" and the potential harms are "greater than anticipated," the editorialists write. "Yet that nuanced balance is not easily communicated."
In short, clinicians face a tremendous task when trying to communicate the risks and benefits of mammography screening to individual patients, they suggest.
They do offer some advice for clinicians who sit and talk with women considering screening: "Messages based on fear or guilt may impede full understanding."
Fifty Years of Data
In their review of 50 years of data, Drs. Pace and Keating conclude that mammography screening is associated with a 19% overall reduction of breast cancer mortality (approximately 15% for women in their 40s and 32% for women in their 60s).
But, for a 40- or 50-year-old woman undergoing 10 years of annual mammograms, the cumulative risk of a false-positive result is about 61%.
Additionally, about 19% of the cancers diagnosed during that 10-year period of mammograms would not have become clinically apparent without screening (and thus represent overdiagnosis). However, Drs. Pace and Keating note that "there is uncertainty about this [overdiagnosis] estimate."
Strong Response From Imaging Societies
The analysis from Drs. Pace and Keating met with fierce opposition from 2 medical societies: the American College of Radiology (ACR) and the Society of Breast Imaging (SBI).
In a joint press release, the 2 groups raise the specter of missed cancers and subsequent deaths.
"Breast cancer screening based primarily on risk — as discussed in the JAMA article — would miss the overwhelming majority of breast cancers present in women and result in thousands of unnecessary deaths each year," the statement reads.
Part of the problem with the study is that it relied too much on old data, the groups assert.
"The JAMA article authors also placed too much emphasis on the obsolete and low lifesaving benefit of mammography claimed in outdated or discredited studies," they state.
As an example, the critics cite the Canadian National Breast Screening Study (CNBSS), which is included in the JAMA analysis. CNBSS has been "widely discredited," and the World Health Organization officially excluded it from their analyses of screening's mortality benefit, according to the ACR/SBI statement.
"More recent" randomized controlled studies, say the 2 societies, "have reconfirmed that regular mammography screening cuts breast cancer deaths by roughly a third," which is about double that claimed by Drs. Pace and Keating, in all women 40 years and older — including women 40 to 49 years. This statement refers to Swedish studies from Hellquist et al andTabár et al, which are, respectively, the largest and longest running randomized trials, the ACR/SBI statement reports.
Dr. Keating countered this criticism. "Selectively reporting results only from the studies that showed the biggest benefits of mammography does not accurately reflect the larger body of research on screening mammography."
However, she conceded that their clinical sources were not perfect. "We agree that there are some limitations to all of the randomized trials of screening."
Nonetheless, in total, the trials cited in the analysis "offer the best data that we have," she added.
Tools at Hand: Decision Aids and Risk Models
Drs. Pace and Keating believe "more research" is needed to "optimize" the 2 primary tools for individualizing screening advice and education to patients: risk models and decision aids. But in the meantime, clinicians have to work with these instruments.
In a section of their review entitled "Individualizing Mammography Screening Decisions," they take a detailed look at both tools.
But first, they set the stage with some grounding statistics.
For a woman in the United States, "the average lifetime risk of breast cancer is about 12.3%; the 10-year risks of invasive breast cancer at ages 40, 50, and 60 years are 1.5%, 2.3%, and 3.5% respectively," they report.
Numerous risk factors have been identified for breast cancer, but "up to 60% of breast cancers occur in the absence of known risk factors," they note.
Nevertheless, attempting to establish a woman's individual risk is important. "The net benefit of screening depends greatly on baseline breast cancer risk, which should be incorporated into screening decisions," Drs. Pace and Keating write.
The Gail model is commonly used in clinical practice to assess a patient's risk. The risk factors incorporated into this model include age at menarche, age at first birth, number of first-degree relatives with breast cancer, number of previous breast biopsies, presence of atypical hyperplasia, and breast density.
But the Gail model and other patient risk models have an underlying fault. Drs. Pace and Keating note that they are "more accurate in predicting incidence in population subgroups and far less useful in identifying which individual women will or will not get cancer."
Nevertheless, they point out that the Gail model has been validated in 3 large populations and is the basis for the National Cancer Institute's online Breast Cancer Risk Assessment Tool.
Informed decisions about mammography screening should include consideration of "patients' values," they note, because these help reconcile information about the risks and benefits of screening.
"Decision aids using pamphlets, videos, or Internet tools can provide information, elicit preferences, and help patients make decisions," they write.
Numerous studies have consistently reported that decision aids provide benefits for patients, including an increased understanding of risks and benefits. However, 3 of the studies showed that the use of decision aids resulted in women having "decreased intentions to be screened," add Drs. Pace and Keating.
"Ideally, patients will be able to use a decision aid before they come to see a physician, and then can discuss what they learned with the physician at the visit," said Dr. Keating.
Dr. Pace's work for this review was funded by the Global Women's Health Fellowship at Brigham and Women's Hospital. Dr. Keating reports receiving research funding from the National Cancer Institute, the American Cancer Society, and the Komen for the Cure Foundation. Dr. Elmore reports serving as medical editor for the Informed Medical Decisions Foundation. Dr. Kramer has disclosed no relevant financial relationships.
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