Breast cancer screening programs can reduce deaths, but will ‘modest’ benefits persist?

A study of Norwegian women invited to a breast cancer screening program indicated that an invitation to undergo modern mammography may reduce breast cancer deaths, but evolving treatments will likely result in a gradual reduction in screening benefit.

An accompanying editorial took the results as another example of the “modest” benefits of screening. Both the study and editorial were published online June 17 in BMJ.

The Norwegian study, led by Harald Weedon-Fekjær, PhD, of the Department of Public Health at the Norwegian University of Science and Technology and the Oslo Center for Biostatistics and Epidemiology at the University of Oslo, aimed to evaluate the effectiveness of contemporary mammography screening given that randomized trials from the 1970s and 80s have become outdated due to advances in care and changes in cancer risk.

To this end, Weedon-Fekjær and colleagues analyzed data from all Norwegian women aged 50 to 79 during 1986 to 2009. Within that period, from 1995-2005, a mammography screening program was gradually implemented that involved biennial invitations to screening for women aged 50 to 69. The authors compared the rates of breast cancer death among those invited to screening with those who had not been invited to screening before being diagnosed with breast cancer.

“Modern treatment has reduced the number of deaths from breast cancer and in the analysis we took into account the effect of changes in nationwide treatment by adjusting for trends in national breast cancer mortality,” they wrote.

With more than 15 million person years of observation, Weedon-Fekjær and colleagues estimated that invitation to mammography screening was associated with a 28 percent reduction in the risk of death from breast cancer. They also estimated that 368 women would need to be invited to screening to prevent one death from breast cancer.

Despite these significant benefits, Weedon-Fekjær and colleagues noted that treatment will continue to improve, likely further reducing the absolute benefit of screening. “The secular decline in breast cancer mortality caused by progress in treatment is substantial, and one consequence of further improvements in treatment is that increasingly more women will need to be invited to mammography screening to prevent one death from breast cancer.”

The accompanying editorial, co-authored by Joann G Elmore, MD, of the University of Washington School of Medicine in Seattle, and Russell P Harris, MD, of the University of North Carolina, Chapel Hill, said the Norwegian study merely confirms that the benefits of screening mammography are “modest at best,” and that women need to be provided with more balanced information.

“While the benefits are small, the harms of screening are real and include overdiagnosis, psychological stress, and exorbitant healthcare costs,” wrote Elmore and Harris.

They noted that the Swiss Medical Board, after reviewing the evidence for breast cancer screening, recommended no new screening programs be introduced as it’s not obvious the benefits outweigh the harms. While much has changed in the 50 years since the first trials on breast cancer screening were launched—including rates of hormone therapy and obesity, as well as screening technology and treatment effectiveness—these changes are glossed over in the ardent promotion of screening. Some hospitals promote screening with “mammogram parties” that include massages and appetizers to pamper attendees.

“In addition to appetizers, we suggest serving women balanced information about the benefits and harms of screening to chew on,” wrote Elmore and Harris.