Benefits and Risks of Mammography Explored in New Analyses

Rosemary Frei, MSc

May 2014, Vol 5, No 4 - Breast Cancer

According to a new systematic review of the risks and benefits of breast cancer screening, regular mammography is associated with a 19% reduction in breast cancer mortality, but it is also associated with a 61% cumulative risk of a false-positive result, and approximately 19% of the cases are, in fact, considered overdiagnoses (Pace LE, Keating NL. JAMA. 2014;311:1327-1335).

The Mammography Conundrum
“We are hopeful that our review will help physicians and patients understand the limitations of mammography and really engage in shared decisions about when to start and how often to have mammograms,” Nancy L. Keating, MD, MPH, Associate Professor of Medicine and of Health Care Policy, Harvard Medical School, and Associate Physician, Brigham and Women’s Hospital, Boston, told Value-Based Cancer Care.

“It’s unfortunate that we don’t have a better test to screen for breast cancer. We need to acknowledge the limitations of mammography and the importance of individualizing these decisions,” said Dr Keating, who shares this view with her colleague, Lydia E. Pace, MD, MPH, Research Fellow in Medicine at Brigham and Women’s Hospital.

In an accompanying editorial, Joann G. Elmore, MD, MPH, University of Washington School of Medicine, Seattle, and Barnett S. Kramer, MD, MPH, Director, Division of Cancer Prevention, National Cancer Institute, noted that “the United States apparently is distinct in having so many groups actively encouraging annual screening starting at age 40 years. Most other countries recommend beginning screening later (eg, age 50) and at less frequent intervals (eg, every 2 to 3 years)” (JAMA. 2014;311:1298-1299).

Dr Elmore and Dr Kramer added that “raising the thresholds for recall and biopsy after mammography, reducing the frequency of screening examinations, and focusing on frequent screenings for only high-risk populations may improve the benefit-harm ratio of screening mammography.”

Screening in Older Women
A review article by Louise C. Walter, MD, Chief of Geriatrics, University of California, San Francisco, and Mara A. Schonberg, MD, MPH, Harvard Medical School, Boston (JAMA. 2014;311:1336-1347), focused on the literature related to women aged ?75 years, who have largely been excluded from randomized controlled trials of screening mammography.

The authors noted that retrospective cohort and case-controlled studies indicate that routine mammography lowers breast cancer mortality in older women. In women aged >80 years, the sensitivity of mammography is 86% and the specificity is 94% compared with 73% and 92%, respectively, in women aged 50 years.

However, just as in younger women, there are significant harms from mammography for older women; in fact, the harms from breast cancer treatment are greater in older women and those with limited life expectancy, according to data cited by Dr Walter and Dr Schonberg. They cited a 2004 study that showed that 97.5% of women in the United States diagnosed with ductal carcinoma in situ undergo surgery.

Dr Walter and Dr Schonberg suggest that physicians explain to older women that “it is not known if mammography decreases the risk of dying from breast cancer in women aged 75 years and older and a choice should be made whether to continue screening. Clinicians should explain this choice in the context of potential benefits and harms related to screening.”

Risk Reduction, Overdiagnosis
Dr Keating and Dr Pace noted that based on a 2011 and a 2013 meta-analysis, the risk ratio for breast cancer mortality reduction with mammography screening in all age-groups is 0.81. This is equal to a 19% mortality reduction. Furthermore, they cited other studies showing a 61.3% 10-year cumulative risk of having at least 1 false-positive result for women undergoing annual mammograms starting at age 40 or 50 years, and a 49.7% false-positive risk for women starting annual mammography at age 66 to 74 years.

And a 2013 meta-analysis of 3 randomized trials—which did not offer screening to the control group—showed that 19% of cancers diagnosed during the screening period were overdiagnoses that comprised ductal carcinoma in situ and some invasive cancer diagnoses. Both types are now considered overdiagnoses, according to Dr Keating and Dr Pace, because their treatment would cause more harm to the patient, without any benefit, because “the tumor would not have caused problems if undetected,” they wrote. “Many authors now describe overdiagnosis as the most concerning potential harm of mammography screening,” they added.

They underlined the need to discuss the “risks, benefits, uncertainties, alternatives, and patient preferences” when discussing mammography intervals with patients.

“It’s important to consider a woman’s risk of breast cancer, because women at higher risk will have greater benefit from mammography,” Dr Keating told Value-Based Cancer Care.

She and Dr Pace believe that decision aids show great promise, noting that a study among American women aged ?75 years showed that those who received a decision aid knew more about the benefits and risks of screening than women who had not received such an aid. These women also are less likely to have a mammogram in the next 2 years. Dr Keating and Dr Pace expect decision aids to become more widely available in the future.