USPSTF issues final recommendations on screening for breast cancer
They apply to asymptomatic women 40 years of age and older who do not have preexisting breast cancer or history of a high-risk breast lesion and who are not at high breast cancer risk due to a known underlying genetic mutation or history of chest radiation as a child.
The U.S. Preventive Services Task Force (USPSTF) issued its final recommendations this week on screening for breast cancer in average-risk women.
The recommendations were based on a review of the evidence on effectiveness of breast cancer screening at reducing mortality from breast cancer and all causes. The incidence of advanced breast cancer and morbidity related to treatment, harms of screening, performance of digital breast tomosynthesis for primary screening, and adjunctive screening in women with dense breasts were also evaluated. In addition, the Task Force considered optimal ages to start and stop screening; the effect of breast density, breast cancer risk, and comorbid conditions; and the association of different screening strategies with radiation-induced breast cancer cases and deaths.
The recommendations were published online Jan. 12 by Annals of Internal Medicine. They apply to asymptomatic women 40 years of age and older who do not have preexisting breast cancer or history of a high-risk breast lesion and who are not at high breast cancer risk due to a underlying genetic mutation or history of chest radiation as a child.
The USPSTF recommends biennial screening mammography for women age 50 to 74 years (B recommendation, meaning there is high certainty that the net benefit is moderate or moderate certainty that the net benefit is moderate to substantial). For women younger than age 50 years, the decision to begin screening mammography should be made on an individual basis, and women who put more value on potential benefit than potential harms of screening may choose to start biennial screening between ages 40 and 49 years (C recommendation, meaning there is at least moderate certainty that the net benefit is small).
The UPSTF concluded that the available evidence is insufficient to assess the balance of benefits and harms of screening in women age 75 years and older, the benefits and harms of digital breast tomosynthesis as a primary screening method, and the benefits and harms of adjunctive screening for breast cancer in women who have dense breasts.
The USPSTF noted that average-risk women ages 50 to 74 years derive the most benefit from biennial screening and that average-risk women ages 60 to 69 years are most likely to avoid death because of screening mammography. Screening mammography may reduce risk for breast cancer death in average-risk women ages 40 to 49 years, but fewer deaths are averted in this age group than in older women, and false-positive results and unnecessary biopsies are more common, the Task Force said. Women who have a family history of breast cancer are at higher risk and may benefit more from screening in their 40s than average-risk women, the Task Force noted. The Task Force also stressed that a C recommendation for screening women ages 40 to 49 years “is not a recommendation against mammography screening in this age group; it signifies moderate certainty of a net benefit for screening that is small in magnitude. A ‘C’ recommendation emphasizes that the decision to screen should be an individual one, made after a women weighs the potential benefit against the possible harms.”
The Task Force's recommendation statement was accompanied by systematic reviews on effectiveness, of breast cancer screening harms of breast cancer screening, and supplemental screening in women with dense breasts, as well as by modeling studies on benefits and harms associated with different screening strategies, radiation-induced breast cancer incidence and mortality from digital mammography screening, and factors associated with false-positive and false-negative digital mammography results.
In addition, an editorial by the Task Force pointed out that while differences in screening recommendations exist, there is also “a strong emerging convergence among groups who have recently issued evidence-based guidelines” suggesting that screening mammography has value for women in their 40s and supporting personal, informed choice for those in their early 40s. “This convergence among distinct organizations, all of which adhere to the rigorous conflict-of-interest standards advanced by the National Academy of Medicine, should give the public confidence in the science that supports mammography screening,” the Task Force authors wrote.
An unrelated article in the same issue of Annals looked at the effect of treatment advances on mortality by comparing the outcomes of breast cancer screening trials conducted using contemporary systemic treatments with outcomes of trials conducted with previously used treatments. The authors used a computer simulation model of 3 virtual screening trials with similar reductions in advanced-stage cancer cases reflecting treatment patterns in 1975 (before chemotherapy), 1999, or 2015 (treatment according to receptor status). At 10 years, screening in a 1975 trial yielded a breast cancer mortality rate ratio (MRR) of 90% and an absolute risk reduction (ARR) of 5 deaths per 10,000 women, while a 2015 screening trial yielded an MRR of 90% and an ARR of 3 deaths per 10,000 women. A greater screening effect was seen with a greater reduction in advanced-stage disease, although MRRs stayed similar across trials. The MRR was 88% when contemporary treatments were available only for early-stage cases. ARRs were consistently lower with contemporary treatments. The authors concluded that therapeutic advances have not substantively reduced relative benefits of screening but have probably reduced the absolute benefits since they have had a positive effect on survival.
The author of an accompanying editorial pointed out that in other trials, relative reductions in risk for breast cancer death have been greater than the relative reductions expected from downstaging, or identifying early-stage cancer, and meta-analyses of breast screening trials have found much higher relative risk reductions than those predicted from reductions in rates of advanced-stage cancer. This raises the question of whether the breast cancer mortality reductions were related to factors other than the ability of screening to prevent advanced-stage disease, the author said. The current study, he wrote, “shows that changes in treatment efficiency over time cannot explain these contrasts. Hence, the factors associated with trial design (for example, the absence of blinding) and statistical analyses probably led to overestimation of the capacity of breast screening to decrease the risk for breast cancer death.”