Mammograms Might Not Reduce Deaths Says Study

Annual mammography screening did not reduce breast cancer deaths

(RxWiki News) If you get an annual mammogram, you are reducing your risk of dying from breast cancer, right? Maybe not, say the authors of a new study challenging this assumption.

This new Canadian study followed a large group of women for 25 years. Some of these women received annual mammograms and some did not.

The researchers found that an annual mammogram for women aged 40-59 was not related to a lower risk of dying from breast cancer. The results have been met with some controversy.

"Talk to your doctor about annual screenings."

This new study, which was led by Anthony B. Miller, MD, of the Dalla Lana School of Public Health at the University of Toronto, utilized data from the Canadian National Breast Screening Study (CNBSS). The CNBSS gathered data at 15 screening centers located in six Canadian provinces during 1980 to 1985.

Dr. Miller and team identified 89,835 women between the ages of 40 and 59. Around half of the women (44,925) received five annual mammogram screenings and the others (44,910 women) received none.

All women above age 50 received annual physical breast examinations, as did women under 50 in the mammogram group. Women under 50 in the non-mammogram group had one physical breast examination and remained in the care of their general doctor.

During the 1980 to 1985 screening period, 666 cases of invasive breast cancers were found in the mammogram group, 180 of which resulted in the patient's death during the 25-year follow-up.

Very similar results were seen in the non-mammogram group. In total, 524 cases of invasive breast cancers were discovered during screening, 171 of which resulted in deaths during the follow-up.

During the entire time period of the study, 3,250 women in the mammogram group and 3,133 in the non-mammogram group were diagnosed with breast cancer. Of these women, 500 of the mammogram group and 505 of the non-mammogram group died of breast cancer, again showing strikingly similar results.

An additional 106 cancers from the mammogram group were determined to be "over-diagnosed" — meaning that one out of every 424 women in the group was given a diagnosis of cancer that the mammogram detected, but that would never clinically develop.

"In conclusion, our data show that annual mammography does not result in a reduction in breast cancer specific mortality for women aged 40 to 59 beyond that of physical examination alone or usual care in the community," wrote Dr. Miller and team.

"The data suggest that the value of mammography screening should be reassessed," they wrote.

However, these conclusions are not without controversy. 

A statement from the American College of Radiology (ACR) called the data source for Dr. Miller and teams's study, the CNBSS, "deeply flawed." According to ACR, the study used machines that were not state-of-the-art and relied on radiologists who were untrained in reading mammography results, among other practices that have been called into question.

"The results of [Dr. Miller's] study, and others resulting from the CNBSS trial, should not be used to create breast cancer screening policy as this would place a great many women at increased risk of dying unnecessarily from breast cancer," urged ACR. 

In an editorial published in response to the study, Mette Kalager, MD, of the University of Oslo in Norway, and colleagues pointed out that other studies have found results different from those described here.

During trials testing mammography screening from the 1960s to 1980s, a reduction in the risk of dying from breast cancer was seen in women between ages 50 and 69 who received mammograms — an estimated 15 to 25 percent lowered risk, wrote Dr. Kalager and colleagues.

It is also important to note that this new study did not take into account any mammograms that potentially occurred after the initial five-year screening period. Further research is needed to explore the relationship between mammograms and breast cancer deaths. 

This study was published February 11 by BMJ. No conflicts of interest were reported.

Review Date: 
February 12, 2014