More than half of women will receive at least one false-positive recall after 10 years of annual screening mammography, according to a study published Oct. 18 in the Annals of Internal Medicine. The findings may fan the flames of the screening debate as an accompanying editorial suggested that the results support screening intervals of two years or more. However, educating women about the incidence of false positives may reduce anxiety, according to the lead author.

The study showed that biennial screening may trim the incidence of false-positive results, and may be linked with a modest increase in the probability of a late-stage diagnosis.

“Our study gives women and physicians information about what to expect over the course of many years of repeat screening mammography. They can use this information along with a woman's individual risk tolerance and information on her personal breast cancer risk to make informed decisions about the best screening strategy for her,” Rebecca A. Hubbard, PhD, assistant investigator with Group Health Cooperative in Seattle, said in an interview.

Given a wide range of figures regarding the likelihood of a false-positive recall, Hubbard and colleagues aimed to estimate the cumulative probability of a false positive recall and biopsy recommendation after 10 years of annual or biennial screening.

The researchers reviewed data from more than 169,000 screening mammograms housed in the seven mammography registries of the Breast Cancer Surveillance Consortium. The mammograms were acquired from women aged 40 to 59 years between 1994 and 2006.

Women who underwent annual screening faced a 61 percent probability of a false-positive result. They reported that 7 to 9 percent of annual screeners received a false-positive biopsy recommendation. Biennial screening cut the probability of a false-positive result to 42 percent.

False positive rates during 10 years of screening were similar for women in their 40s and 50s. However, women who begin screening at age 40 are more likely to receive a false-positive result than women who start screening at age 50 because of the extra decade of screening, according to Hubbard and colleagues.

However, certain factors can reduce the likelihood of a false-positive result.

“An important finding of our study was the substantially decreased risk of false-positive results when comparison films were available. Breast imagers should encourage women to ensure that their previous mammogram is available,” Hubbard said.

The researchers reported that digital mammography improved cancer detection for premenopausal women in their 40s with dense breasts, but it also resulted in a slightly higher rate of false positives than film mammography among these women.

Breast imagers can use the data to provide patients with context about false positives. “Women should understand that false-positive results are common after many years of screening. We hope that by helping women know what to expect when they participate in regular screening mammography they'll feel less anxiety if they are recalled for additional testing,” Hubbard added.

However, editorialist Philippe Autier, MD, of the International Prevention Research Institute in Lyon, France, considered the current data in conjunction with previous findings.

Autier reviewed the Breast Screening Frequency Trial in the U.K. and a study comparing annual screening in Vermont and biennial screening in Norway, and wrote, “Taken together, available evidence does not demonstrate that a shorter interval prevents advanced disease or reduces breast cancer mortality. However, as Hubbard and colleagues demonstrate, a shorter screening interval leads to more false-positive screening results and may also lead to greater detection of small, non-life threatening cases of cancer. In summary, current evidence indicates that mammography screening every year is less efficient than screening every two years or more.”