A pair of studies published in the Annals of Internal Medicine help clarify the risks and benefits of different breast cancer-screening strategies, and explain the US Preventive Services Task Force (USPSTF)’s final recommendation that women should undergo biannual breast cancer screening starting at age 50.1-3 The new research also spotlighted the importance of breast size and breast density in cancer screening.
Digital mammography is safe, posing a small risk of radiation-associated breast cancer for most women, and screening mammography overall prevents many more cancer deaths than it may cause. But some groups of women face increased risk, according to a comprehensive modeling study published in the Annals of Internal Medicine.2
“We found that women with large breasts were at increased risk of radiation-induced cancer because it may be necessary to obtain extra mammographic views to completely image their breasts,” coauthor Rebecca Hubbard, PhD, told Cancer Therapy Advisor. Women with large breasts receive more than twice the radiation dose as those with small breasts, the team found.
“One way to reduce this risk is to make sure that mammography facilities are using larger detectors that can completely image large breasts without requiring additional views,” added Dr Hubbard, who is an associate professor of biostatistics at the University of Pennsylvania’s Perelman School of Medicine in Philadelphia, PA.
“Digital breast tomosynthesis or 3D mammography also has the potential to decrease radiation-induced breast cancer because data suggest that fewer women receiving tomosynthesis are recalled for additional mammography compared to traditional 2D mammography.”
“Fewer recalls means less exposure to radiation and decreased risk of radiation-induced cancer,” she noted.
The role of breast implants was not considered in the study, but it stands to reason that implant-augmented breasts entail similarly increased risks from increased screening views, the coauthors noted.
Biennial rather than annual screening mammography can reduce patients’ radiation-induced cancer risk; so can starting mammographies at age 50 instead of ages 40 or 45, the research team found—part of the rationale for new USPSTF recommendations released January 12, 2016, advising that women should undergo biannual breast cancer screening starting at age 50.1-2
“We estimated that over the course of a lifetime, annual screening from age 40 to 74 induces 125 cancer cases per 100 000 women screened,” Dr Hubbard explained. “Moving to biennial screening from age 50 to 74 decreased this to 27 cases per 100 000 women.”
Given that the United States currently has an estimated 20 million women aged 40 to 49 years, adopting a biennial screening strategy nationwide at age 50 rather than annual screening beginning at age 40 would result in an estimated 20 000 fewer cancer cases, Dr Hubbard said.
“For most women, the risks are very low,” emphasized lead study author Diana Miglioretti, PhD, a professor of biostatistics at the UC Davis School of Medicine in Sacramento, CA. “The one group I worry about is women with very large breasts who choose to be screened annually from age 40 to 74. Most screening mammograms are 2 views per breast. Some women with large breasts need more than 4 views for a complete screening examination, increasing their exposure to ionizing radiation.”4
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Radiation dose per view also increases with compressed breast thickness, “further increasing exposure,” Dr Miglioretti added.
In a separate systematic review of the reproducibility of Breast Imaging Reporting and Data System (BI-RADS) density categorizations, conducted for the USPSTF, Dr Miglioretti and coauthors found that breast density determinations are frequently unreliable, with nearly 1 in 5 women’s categorization as having dense or non-dense breasts changing between mammography examinations.3