Mammography Screening Reduces Rate of Advanced and Fatal Breast Cancer

A contemporaneous comparison of women participating in breast cancer screening versus those not participating found that mammography screening reduces the rate of advanced and fatal breast cancers.¹

The study, published in Cancer, also found that these benefits appeared to be independent of recent changes in treatment regimens.  

“This study shows that participation in breast cancer screening substantially reduces the risk of having a fatal breast cancer,” Stephen Duffy, MSc, from Queen Mary University in London, said in a press release.² “Because the comparison of participating with non-participating persons was contemporaneous - with mammography screening and breast cancer treatment belonging to the same time period - it is not affected by potential changes in treatment of breast cancer over time.”

Of 549,091 women, representing approximately 30% of the Swedish screening-eligible population, the researchers calculated the incidence rates of 2,473 breast cancers that were fatal within 10 years after diagnosis and the incidence rates of 9,737 advanced breast cancers (defined as invasive breast cancer measuring >20 mm and/or with ≥4 metastatic axially lymph nodes). Moreover, data on each breast cancer diagnosis and the cause and date of death of each breast cancer case were collected from national Swedish registries. Tumor characteristics were gathered from regional cancer centers. 

Ultimately, women who participated in mammography screening were found to have a statistically significant 41% reduction in their risk of dying of breast cancer within 10 years (relative risk, 0.59; 95% CI, 0.51-0.68; P < 0.001) and a 25% reduction in the rate of advanced breast cancers (relative risk, 0.75; 95% CI, 0.66-0.84; P < 0.001). Even further, a conservative estimate suggested a significant 34% reduction in cancers that were fatal within 10 years among screening participants. 

“With the introduction of adjuvant breast cancer therapies, there has been speculation regarding the relative contribution of screening versus therapy to the observed reduction in breast cancer mortality, and whether the importance of early detection in reducing breast cancer deaths will diminish as newer therapies are introduced,” the authors wrote. 

“However, the methodology applied in the current study to measure the incidence of breast cancers that were fatal within 10 years after diagnosis overcomes this limitation because in each diagnosis year, patients with breast cancer who have participated and not participated in screening receive treatment according to the same protocols appropriate for their stage of disease at the time of diagnosis, regardless of detection mode,” the authors continued. “Thus, changes in therapy cannot account for the current study results.” 

According to the researchers, these study results also indicated the feasibility of collecting this screening data on a national basis, thereby facilitating more detailed studies of screening performance over time. This sort of prospective data on a large scale would be useful in evaluating new techniques implemented for screening purposes, for which long-term follow-up and large statistical precision is critical. 

“Some may believe that recent improvements in breast cancer treatment makes early detection less important,” László Tabár, MD, of Falun Central Hospital in Sweden, said in a press release. “Our study shows that nothing can replace finding breast cancer early.”

References:

1. Duffy SW, Tabár L, Yen AM, et al. Mammography Screening Reduces Rates of Advanced and Fatal Breast Cancers: Results in 549,091 Women. Cancer. doi:10.1002/cncr.32859. 

2. Early Mammography Screening Lowers Risk of Developing Fatal Breast Cancer [news release]. Sweden. Published May 11, 2020. newsroom.wiley.com/press-release/cancer/early-mammography-screening-lowers-risk-developing-fatal-breast-cancer. Accessed May 12, 2020.