Risks and Benefits of Annual Mammograms

Screening mammography may reduce breast cancer deaths but comes with false positive risk

(RxWiki News) Many more women undergo annual mammograms than are diagnosed with breast cancer, and the screening comes with potential risks.

A recent review quantified some of the harms and benefits of annual mammograms using previous trials and studies.

The researchers found that, while mammogram screenings probably reduce the risk of death from breast cancer, women face the risk of false positives.

These researchers suggested that women use the research to decide for themselves whether to pursue or not pursue a cancer screening.

"Talk to your doctor about the benefits and harms of mammograms."

H. Gilbert Welch, MD, MPH, and Honor J. Passow, PhD, of The Dartmouth Institute for Health Policy and Clinical Practice in The Geisel School of Medicine at Dartmouth, led this review on mammograms.

Mammography involves the use of X-rays to screen for breast cancer.

The National Cancer Institute recommends that women who are 40 or older have screening mammograms every one to two years.

Some risks accompany mammogams, including the possibility that a person could receive a false negative, a false positive, a false alarm or an overdiagnosis (a diagnosis of a disease that is not harmful) that would lead to unnecessary treatment.

The authors of this review attempted to quantify the benefits and the possible harms of screening mammography. According to the researchers, "We hope that these ranges help women to make a decision: either to feel comfortable about their decision to pursue screening or to feel equally comfortable about their decision not to pursue screening."

These authors focused on three outcomes for women at age 40, 50 and 60 who receive annual mammograms: reduction in deaths from breast cancer, false positives and overdiagnosis.

Using previous research, the authors of this study set ranges of risks and benefits based on the most optimistic and pessimistic study results.

To find out how many breast cancer deaths were avoided due to annual screening mammography, the researchers used information from nine previous trials.

The most optimistic result came from a Swedish trial, which estimated that annual mammograms reduced breast cancer mortality by 36 percent.

The trial that reported the lowest risk reduction was a Canadian study that found no death reduction due to mammography. The authors found that result implausible and opted for a 5 percent risk reduction as the lower bound.

The researchers concluded that, of 1,000 women who are 50 years old and undergo annual screening mammography for 10 years, between 0.3 and 3.2 women will avoid death from breast cancer.

To determine the frequency of false positives, the researchers examined a previous study investigating false alarms over 10 years of annual screenings.

That study, conducted in 2011, looked at 170,000 women in their 40s and 50s who received yearly mammograms.

The authors of the study compared false positive rates of women seeing radiologists who were more and less likely than average to call patients back for additional screening, usually involving a biopsy (removal of cells or tissues).

On the higher end of the range, the researchers reported that 490 to 670 per 1,000 women may receive a false positive result.

On the lower end, they estimated that 70 to 100 women per 1,000 would come back for a false positive biopsy.

Lastly, the researchers set high and low bounds for the risk of overdiagnosis due to annual mammographies.

For the lower bound, they used a 15-year follow-up study of women who received mammograms every 18 to 24 months in the 1970s and 1980s.

The study found that over ten years, three per 1,000 women in their 50s would be overdiagnosed. Over the same period, six per 1,000 women in their 60s would be overdiagnosed and have unnecessary treatment.

Recent observational research was used to estimate the upper bounds of overdiagnosis. The authors of the review used the estimate that one-third of all breast cancers are overdiagnosed.

The researchers concluded that the upper bound of overdiagnosis risk was 11 overdiagnoses per 1,000 women in their 40s, 14 for women in their 50s and 20 for women in their 60s.

"According to the study, mammography can reduce a small numbers of breast cancer related deaths but at significant risks of false alarms and over-diagnosis. However, the study did not address the potential benefits of mammography in preventing later stage cancers, which generally require more aggressive treatments such as lymph node dissection, radiation and chemotherapy," said Chi Pham, MD, a medical oncologist with Texas Oncology and a member of the medical staff at Baylor All Saints Medical Center at Fort Worth.

"Since the main obstacle to screening is the false positive rates, newer modalities such as tomosynthesis may be helpful for some women to reduce these false positive rates, therefore tipping the scale in favor of screening," she said.

The authors of this review acknowledged several limitations. For example, their analysis only examined three outcomes of mammography, while other benefits and harms exist.

The authors also noted that more research on the specific benefits of screening mammographies is necessary.

This study was published in JAMA Internal Medicine on January 30.

The authors disclosed no conflicts of interest. No funding information was reported.

Review Date: 
December 30, 2013