During 10 years of receiving mammograms, more than half of cancer-free women will be among those called back for more testing because of false-positive results, and approximately one in 12 will be referred for a biopsy. Screening every other year lowers a woman’s changes of having one of these false-positive episodes by approximately one-third--from 61% to 42%--over the time line of a decade.

A new study probing into false-positives in mammography looked at almost 170,000 women between the ages of 40 and 59 from seven regions around the United States, and nearly 4,500 women with invasive breast cancer. Because of the added decade of testing alone, it found, women who begin mammogram screening at 40 instead of 50 are more likely to have false-positive results that lead to more testing.

“This study provides accurate estimates of the risk of a false-positive mammography and breast biopsy for women undergoing repeat mammography in community practice, and so provides important information about the potential harms of undergoing regular mammography,” said coauthor Dr. Karla Kerlikowske, a professor of medicine at the University of California, San Francisco (UCSF) School of Medicine (USA).

The study’s findings are slated be published in the journal Annals of Internal Medicine. The research was led by Group Health Research Institute of Seattle (WA, USA) for the Breast Cancer Surveillance Consortium (Bethesda, MD, USA). “Recalls” for a second mammogram for what turn out to be false-positives may cause inconvenience and worry. Recommendations for fine-needle aspiration or surgical biopsy are less common, but can lead to unnecessary pain and scarring. The additional testing also contributes to rising medical costs.

Dr. Kerlikowske is the lead author of an additional report--to be published in the same issue of Annals--that for the first time in the United States evaluates the accuracy of film mammography against digital, which has increasingly replaced older film screening. That study examined nearly 330,000 women between the ages of 40 and 79. The information was gathered from the Breast Cancer Surveillance Consortium, a collaborative network of mammography registries in the United States.

The researchers found that overall cancer detection rates were similar for both techniques. However, digital screening may be better for women between the ages of 40 and 49 who are more likely to have extremely dense breasts associated with lower cancer detection. The study also found new evidence that digital mammography is better at detecting estrogen receptor-negative tumors; specifically in women aged 40 to 49 years.

Breast cancer may not be found, the researchers warned, if a radiologist cannot detect a visible breast lesion or if a tumor is hidden by normal breast tissue. Moreover, an indiscernible tumor may grow rapidly and be found through a clinical exam prior to the next mammogram.

Digital mammography was developed in part to improve the detection of breast cancer in dense breasts by improving the ability to distinguish normal dense breast tissue from isodense invasive cancer. The investigators noted that for every 10,000 women 40 to 49 who is given digital mammograms, two more cases of cancer will be identified for every 170 additional false-positive examinations.

Healthy women will undergo 12 screening mammograms in their lifetimes if they follow US Preventive Services Task Force guidelines that recommend biennial screening starting at age 50 and continuing until age 74. This is debatable, with many practitioners recommending annual mammograms. If women start biennial screening at 40, they will undergo 17 exams; those who start annual screenings at age 40 will undergo 34 exams.

For the false-positive study, the investigators discovered that after 10 years of yearly screening, a majority of women will receive at least one false-positive result, and 7% to 9% will receive a false-positive biopsy recommendation. “We conducted this study to help women know what to expect when they get regular screening mammograms over the course of many years,” said study leader Rebecca Hubbard, PhD, an assistant investigator at Group Health Research Institute. “We hope that if women know what to expect with screening, they’ll feel less anxiety if--or when--they are called back for more testing. In the vast majority of cases, this does not mean they have cancer.”

The researchers reported that screening every other year would likely decrease the chance of false-positive findings “but could also delay cancer diagnosis.”' However, for those diagnosed with cancer, the researchers found women screened every two years were not considerably more likely to be diagnosed with late-stage cancer compared to those screened at one-year intervals.

The study emphasizes the importance of radiologists being able to review a patient’s earlier mammograms because it “may halve the odds of a false-positive recall.”

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