How effective is screening mammography for preventing breast cancer mortality?

EXPERT COMMENTARY

Although recommending screening mammograms continues to represent the standard of care, studies from the United States and abroad have questioned their value.^1-3

In the June issue of JAMA Network Open, Australian investigators assessed the relative impacts of mammography screening and adjuvant therapy on breast cancer mortality, using data from population-based studies from 1982 through 2013.⁴ In recent decades, screening has increased substantially among Australian women.

Details of the study

Burton and Stevenson identified 76,630 women included in the Victorian Cancer Registry with invasive breast cancer in the state of Victoria, where women aged 50 to 69 are offered biennial screening.⁴ During the study’s time period, the use of adjuvant tamoxifen and chemotherapy increased substantially.

In the 31-year period assessed in this study, breast cancer mortality declined considerably. During the same period, however, the incidence of advanced breast cancer doubled.

These findings from Australia parallel those from the United States, Holland, and Norway, where the incidence of advanced breast cancer was stable or increased after screening mammography was introduced.^1-3

According to Burton and Stevenson, the increased incidence of advanced cancer clarifies that screening mammography is not responsible for declining breast cancer mortality, but all of the decline in mortality can be attributed to increased uptake of adjuvant therapy.

The authors concluded that since screening mammography does not reduce breast cancer mortality, state-sponsored screens should be discontinued.

Study strengths and limitations

Relevant data for this study were obtained from large population-based surveys for premenopausal and postmenopausal women with breast cancer.

The authors noted, however, that this analysis of observational data examining time trends across the study period can show only associations among breast cancer mortality, mammography screening participation, and adjuvant therapy uptake, and that causality can only be inferred.

The study in perspective

Although some will view the findings and recommendations of these Australian authors with skepticism or even hostility, I view their findings as good news—we have improved the treatment of breast cancer so dramatically that the benefits of finding early tumors with screening mammography have become attenuated.

Although it is challenging given the time constraints of office visits, I try to engage in shared decision making with my patients regarding when to start and how often to have screening mammography. ●