Women who underwent routine mammography screening demonstrated a 60% lower risk for dying of breast cancer within a decade of diagnosis than women who did not participate in screenings, according to a study published in Cancer.
The mortality risk for women who participated in organized breast cancer screening programs was 47% lower within 20 years of diagnosis.
“In the context of breast cancer screening and its effect on breast cancer mortality, the issue is that exposure or not to screening pertains to the time of diagnosis, whereas the endpoint — death from breast cancer — takes place years later,” Laszlo Tabar, MD, professor of radiology at University of Uppsala School of Medicine and medical director emeritus in the department of mammography at Falun Central Hospital in Sweden, and colleagues wrote. “To overcome this disparity, we have used a new methodology to improve the evaluation of the impact of organized mammography screening on death from breast cancer.”
Tabar and colleagues analyzed data from comprehensive registries on screening history, breast cancer incidence and disease-specific mortality of more than 52,000 women aged 40 to 69 years in Dalarna County, Sweden. The researchers determined the annual incidence of breast cancer — as well as annual incidence of cases that were fatal within 10 years and within 11 to 20 years — among women who did and did not participate in a mammography screening program between 1977 and 2015.
They compared the results with matching data from the prescreening period between 1958 and 1976.
All women underwent stage-specific treatment according to the latest national guidelines, regardless of the mode of detection.
The study period spanned 58 years. During that time, 4,513 women were diagnosed with breast cancer.
Investigators obtained 20 years of follow-up data on 3,231 women (1,225 in the prescreening period and 2,006 in the screening period through 1995), as well as 10 years of follow-up data on 1,281 women diagnosed with breast cancer between 1996 and 2005.
Results showed 1,061 women died of breast cancer within 10 years of diagnosis (552 in the prescreening period and 509 in the screening period). An additional 214 women died of breast cancer 11 to 20 years after diagnosis.
Women who opted to participate in an organized breast cancer screening program had a 60% lower risk for dying of breast cancer within 10 years of diagnosis (RR = 0.4; 95% CI, 0.34-0.48) and a 47% lower risk for dying of breast cancer within 20 years of diagnosis (RR = 0.53; 95% CI, 0.44-0.64) than nonparticipants. An analysis adjusted for possible self-selection bias still showed a significant decrease in the risk for breast cancer mortality within 20 years of diagnosis associated with screening participation (RR = 0.55; 95% CI, 0.45-0.67).
Such findings give more reasons why [our institution’s] department of radiology and biomedical imaging supports annual mammography screening starting at age 40 to save more lives,” Bonnie Joe, MD, PhD, professor in residence and chief of breast imaging at University of California, San Francisco, said in a press release. “A combination of screening and therapy are essential. Earlier screening leads to more effective therapy.” – by Jennifer Byrne
Disclosures: Tabar reports honoraria, travel and personal fees from General Electric Healthcare, and personal fees from Mammography Education Inc. and Three Palm Software, all outside the submitted work. Please see the study for all other authors’ relevant financial disclosures.