• Posted November 3, 2023

False-Positive Mammogram Result Raises Odds for Breast Cancer Later

Women who have a false-positive result on a screening mammogram may have an increased risk of breast cancer for up to 20 years, a large new study finds.

False-positives occur when a screening mammogram seems to show something abnormal that, with follow-up testing, is declared non-cancerous.

The new study -- published online Nov. 2 in JAMA Oncology -- suggests those screening results can be more than a false alarm. For some women, they may signal a relatively heightened risk of breast cancer in coming years.

The link between false-positives and future breast cancer was strongest among older women (age 60 and up) and women with low breast density, which means the breasts have more fat tissue than fibrous and glandular tissue.

Experts said the findings underscore the importance of continuing to get regular breast cancer screenings after a false-positive result -- even though that experience might make some women hesitant.

"It's important for these women to maintain long-term awareness of breast cancer," said study leader Xinhe Mao, a researcher at the Karolinska Institute in Stockholm, Sweden. "They should continue attending regular mammography screenings and remain vigilant about breast symptoms and changes in breast appearance."

The findings are based on nearly 500,000 Swedish women who underwent mammography screening between 1991 and 2017. The group included more than 45,000 women who had received a false-positive result.

Over 20 years, 11% of women in that false-positive group later developed breast cancer, versus 7% of women without a false-positive.

When Mao's team dug deeper, they found that age and breast density were important factors. Among women aged 60 to 75, those with a false-positive had double the risk of later developing breast cancer compared to those with no history of a false-positive. The risk linked to false-positives was less among younger women.

Meanwhile, breast density was even more important. Among women with low breast density, those with a false-positive mammogram were nearly five times more likely to eventually be diagnosed with breast cancer.

In contrast, there was no strong link between false-positives and later breast cancer risk among women with dense breasts.

That finding is "novel," Mao said, but it's not surprising.

False-positive results are more common among women with dense breasts because that non-fatty tissue makes mammograms harder to read. So those women, Mao said, are often called back for follow-up testing simply because it was hard to distinguish normal from abnormal tissue on the initial mammogram.

When women have low breast density, though, that call-back may more often be due to a truly suspicious finding, Mao said. And even though they may then be told it's a false-positive result, they could still be at increased risk of breast cancer in the future -- because a tiny tumor was missed, for example, or because they have a "proliferative" breast condition.

Those conditions, which make breast cells look abnormal, are not cancerous, but are tied to a heightened risk of breast cancer.

"This study underscores the importance of continued, regular screening mammograms," said Susan Brown, senior director of health information and publications at the breast cancer nonprofit Susan G. Komen.

Brown, who was not involved in the study, said there is no blanket advice for women who have had a false-positive result. Instead, she said, women should talk to their doctor about their personal risk of breast cancer and "the screening plan that is right for them."

Mao agreed, and said that more research is needed to show whether women who receive a false-positive result can benefit from more "intensive" screening for a time afterward. In this study, the increased breast cancer risk was greatest in the four years following a false-positive mammogram.

A caveat is that the study was done in Sweden, where women undergo mammography screening every two years. In the United States, yearly mammograms are often recommended.

False-positive results, meanwhile, are much more common in the United States. It's estimated that half of U.S. women will have at least one false-positive result after 10 screening mammograms, versus 20% of their European counterparts.

According to Mao, that may be due in part to more-frequent screening. But U.S. providers may also be more likely to flag mammograms as abnormal.

Mao said her team thinks the general pattern seen in this study would hold true in the United States, too. But the breast cancer risk associated with false-positive mammograms might be less.

More information

The American Cancer Society has a primer on mammography screening.

SOURCES: Xinhe Mao, MSc, researcher, medical epidemiology and biostatistics, Karolinska Institute, Stockholm, Sweden; Susan Brown, MS, RN, senior director, health information and publications, Susan G. Komen, Dallas; JAMA Oncology, Nov. 2, 2023, online