Screening mammography may benefit younger women with increased breast cancer risk

Screening mammography may have more benefit than harm in women 40 to 49 years of age who are at increased risk for breast cancer, according to two new studies published in today's Annals of Internal Medicine.

In a systematic review and meta-analysis, researchers evaluated data from 66 published articles and from the Breast Cancer Surveillance Consortium to determine what factors were associated with increased breast cancer risk in women 40 to 49 years of age. Extremely dense breasts and a first-degree relative with breast cancer were each associated with at least a 2-fold increase in risk. Previous breast biopsy, heterogeneously dense breasts and second-degree relatives with breast cancer were each associated with a 1.5- to 2-fold increased risk, while current oral contraceptive use, nulliparity, and age 30 or older at first childbirth were each associated with a 1.0- to 1.5-fold increased risk.

The authors noted that they did not assess effects of multiple risk factors and that the included studies varied in measures, reference groups, and adjustment for cofounders. However, they concluded that their analysis identified two important potential risk factors for breast cancer in women age 40 to 49 years: very dense breasts and first-degree relatives with breast cancer. Clinicians and patients may want to consider this information when deciding on personalized screening, they said.

In the second study, researchers used four independent models to determine the threshold relative risk (RR) at which the harm/benefit ratio of screening mammography in women age 40 to 49 years equals that of biennial screening in women age 50 to 74 years. Mammography screening starting at age 40 was compared with mammography screening starting at age 50 using digital or film mammography. Annual and biennial screening intervals were also compared to determine which approach yielded the most benefits (life-years gained, breast cancer deaths averted) and least harms (false-positive results).

For women age 40 to 49 with a 2-fold increased risk for breast cancer, the harm/benefit ratio of biennial screening with digital mammography (defined as false-positive findings/life-years gained) was similar to that of biennial screening in average-risk women age 50 to 74 years (median threshold RR, 1.9 [range across models, 1.5 to 4.4]). The threshold RRs were higher for annual digital mammography (median, 4.3 [range, 3.3 to 10]), as well as for a harm/benefit ratio defined as false-positive findings/deaths averted rather than false-positive findings/life-years gained. Film mammography had a more favorable harm/benefit ratio than digital mammography because it has a lower false-positive rate, the authors noted.

The study considered false-positive results as the only potential harm from screening and did not take differences in preferences between older and younger women into account, among other limitations. However, the authors concluded that biennial screening starting at age 40 has more benefit than harm in women whose risk for breast cancer is twice as high as average.

In an editorial accompanying both studies, the chief medical and scientific officer and executive vice president of the American Cancer Society stressed the need for further education about risks and benefits of mammography since future guidelines for screening will likely be tailored to the individual.

“This will be challenging because many health care providers and members of the lay community do not understand screening and the concept of risk,” he wrote. “Specific tools designed to educate them need to be developed and rigorously assessed. Ultimately, the preferences of individual women, recognizing the potential for harm and benefit, should be respected.”