Since 1989, the combination of mammography and improved breast cancer treatment has averted hundreds of thousands of breast cancer mortalities for U.S. women, according to new research published online Feb. 11 in the journal Cancer.
A multi-institutional team of researchers led by R. Edward Hendrick, PhD, of the University of Colorado School of Medicine in Aurora, Colorado, found that since screening mammography became widely available in the mid-1980s, up to 614,500 breast cancer deaths have been prevented.
“Recent reviews of mammography screening have focused media attention on some of the risks of mammography screening, such as call-backs for additional imaging and breast biopsies, downplaying the most important aspect of screening—that finding and treating breast cancer early saves women's lives,” Hendrick said in a prepared statement. “Our study provides evidence of just how effective the combination of early detection and modern breast cancer treatment have been in averting breast cancer deaths.”
To estimate the number of lives saved, Hendrick and colleagues analyzed five-year breast cancer mortality data and female population data for U.S. women aged 40 to 84 years over the past three decades from the Surveillance, Epidemiology, and End Results (SEER) database. The team then estimated background breast cancer death rates (in the absence of screening mammography and improved treatment) using the following four methods:
- Background mortality rates were assumed to be flat since 1989.
- Assumed background mortality rates after 1989 continued their previously steady increase of 0.4 percent per year.
- Background mortality rates after 1989 were estimated for each five-year age group using the change in mortality rates for that age group prior to 1990.
- The background breast cancer mortality rates were assumed to increase by .94 percent per year since 1989.
Additionally, the researchers estimated the mortality reduction percentage for U.S. women overall and separated those figures into five-year age groups. They also assumed, that for each of the four methods, the background mortality rate change continued from 1989 to different end dates of 2012, 2015 and 2018.
“Estimates for 2012 and 2015 are based entirely on SEER breast cancer mortality rate and population data,” Hendrick et al. wrote. “Estimates for 2018 are based on extrapolations of SEER breast cancer mortality rates and census projections of US female population data from 2016 to 2018.”
Once they determined the number of breast cancer deaths averted in a certain year, the team added up deaths averted each year from 1990 to 2012, 2015 and 2018.
The study did have its limitations, however, including that SEER breast cancer incidence data does not specify whether a woman attended mammography screening within one year of her breast cancer diagnosis. Additionally, the researchers did not attempt to estimate the separate contributions of screening versus advances in treatment.
The researchers also estimated the number of breast cancer deaths averted and percentage mortality reduction since 1989, instead of total breast cancer deaths averted by screening mammography and treatment. The team noted that although the onset of widespread screening mammography in the mid-1980s didn’t begin to affect breast cancer mortality rates until the early 1990s, treatment improvements such as tamoxifen and surgical therapy advances were ongoing and averting breast cancer mortality before 1989.
“However, based on SEER mortality data and the estimates in the current study, we believe that hundreds of thousands of women’s lives, likely in excess of one-half million by 2018, have been saved by the use of screening mammography and new developments in breast cancer treatment since 1989,” the researchers wrote.
The researchers concluded that more clinical benefits will likely be unearthed as research continues.
“While we anticipate new scientific advances that will further reduce breast cancer deaths and morbidity, it is important that women continue to comply with existing screening and treatment recommendations,” co-author Mark A. Helvie, MD, of the University of Michigan Health System in Ann Arbor, Michigan, said in a statement.