Screening mammography reduces risk of breast cancer death in 10 years by 60%
Diagnosing breast cancer in its earliest stages makes curative treatment regimens more effective with respect to recovery and overall survival. A new study of more than 52,000 Swedish women that calculated the annual incidence of breast cancers causing death within 10 and 20 years of diagnosis reconfirms the importance and value of regular breast cancer screening. Women who had regular screening mammograms had a 60% lower risk of dying from breast cancer within 10 years and a 47% lower risk within 20 years, according to findings published online November 8th in Cancer.
Principal investigator Lásló Tabár, MD, of the department of mammography in Falun Central Hospital in Falun, Sweden, and a multinational team of researchers contend that the incidence of breast cancer deaths provides a direct measure of the impact of regular mammography screening. This method eliminates length bias, because the denominator in the calculation is the mid-year population of women, not breast cancer cases. In the year of diagnosis, women receive the treatment that is standard for their stage of diagnosis regardless of detection mode, eliminating the variable influences of changes in therapy over time. The 20-year cutoff was selected because approximately 95% of breast cancer deaths occur within this time frame, thus reducing nearly all potential influence of lead time.
The study included all women aged 40 to 69 who lived in Dalarna County, Sweden, between 1958 and 2015. Data were obtained from the Swedish Cancer Registry for all women diagnosed with breast cancer starting in 1958 and from the National Death Registry of the Swedish National Board of Health and Welfare. Data about mammography screening participation were obtained from a population-based, organized mammography screening program in Dalarna County that began in October 1977. The authors reported that a total of 3,231 women out of 4,513 diagnosed with breast cancer could be followed for 20 years during the 58-year time span of the study.
The researchers calculated the annual incidence of breast cancer diagnosis and breast cancer death per 100,000 women aged 40-69 at age of diagnosis in the 19-year prescreening time frame between 1958 through 1976, and the mammography screening availability time frame between 1977 through 2015. Only 15% of women of this very stable population did not elect to participate in the mammography screening program.
The authors also addressed the debate that exists over the relative impact of screening versus modern therapy in reducing the risk of breast cancer mortality. In each year of diagnosis, women receive the stage-specific therapy that reflects standard treatment. This is irrespective of the mode of diagnosis or whether the women did or did not participate in regular breast cancer screening.
Co-author Robert Smith, PhD, vice president of cancer screening of the American Cancer Society, commented to Applied Radiology, “The observed, substantial breast cancer mortality reductions associated with exposure to screening indicate that women who participate in regular screening stand to benefit more from that state-of-the-art therapy at the time of diagnosis compared with women who do not attend screening. The debate over which contributes more, screening vs. therapy, is unproductive, and distracts from the clear evidence that women benefit most when they attend screening and receive state-of-the-art therapy.”
“Although much attention has been devoted to the potential ‘harms’ of participating in regular screening, little attention has been given to the harms of not participating in regular screening, the greatest harm being a significantly increased risk of death from breast cancer,” the authors stated. “Our results, from precise, individual-based data covering 6 decades, should provide women and their physicians with reassurance that participating in regular, high-quality mammography screening is the best way to reduce the risk of a premature death from breast cancer.”
REFERENCE
- Tabár L, Dean PB, Chen TH, et al. The incidence of fatal breast cancer measures the increased effectiveness of therapy in women participating in mammography screening. Cancer. Published online November 8, 2018. doi: 10.1002/cncr.31840.