Mammography screening doesn't lower risk of breast cancer death

Tuesday June 10, 2014 (foodconsumer.org) -- Doctors promote mammography screening for breast cancer because THEY believe that with mammography screening, the disease can be diagnosed earlier, and get treated earlier and the disease can have a better prognosis.

Unfortunately, a new Canadian study published in British Medical Journal suggests that annual mammogram screening for breast cancer does not reduce risk of death from the disease.  Some early studies have come to the same conclusion.

Anthony B Miller at Dalla Lana School of Public Health, University of Toronto in Toronto, Canada and colleagues followed women aged 40 to 59 years who did or did not undergo mammography screening for up to 25 years and found the screening did not reduce mortality from breast cancer.

Data used for the study came between 1980 and 1985 from 15 screening centers in six Canadian provinces including Nova Scotia, Quebec, Ontario, Manitoba, Alberta, and British Columbia.  A total of 89,835 women aged 40 to 59 years of age were randomly assigned to receive mammography screening (five annual screens) or no mammography.

For the study, "women aged 40-49 in the mammography arm and all women aged 50-59 in both arms received annual physical breast examinations. Women aged 40-49 in the control arm received a single examination followed by usual care in the community."

During the five-year screening period, a total of 666 invasive breast cancers out of 44, 925 women were diagnosed in the mammography arm, compared to 524 out of 44, 910 women in the control group.

And of those diagnosed with breast cancer, 180 women in the mammography screening arm and 171 women in the control arm died of the disease, during the 25-year follow-up period.

As a result, the relative risk of death from breast cancer associated with mammography, compared to that found in those who did not use the screening was 1.05, meaning both arms had a similar death risk.

Incidence of breast cancer was also found similar in both arms.

And after 15 years of follow-up, 106 cases of breast cancer were over-diagnosed in the mammography screening arm.

The researchers concluded annual mammography screening in women aged 40 to 59 years does not reduce risk of death from breast cancer when subjects were given usual physical examination or care and adjuvant therapy when needed.

The study also suggests that as many as 22% of screen detected invasive breast cancers were over-diagnosed.   That is, one in every 424 women was over diagnosed with breast cancer when mammography screening was used.  (David Liu, PHD)

Reference

Anthony B Miller, Claus Wall, Cornelia J Baines, Ping Sun, Teresa To, Steven A Narod, Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial.  BMJ 2014;348:g366