Breast cancer Mortality No Longer Declining For U.S. Women Under 40

Breast cancer mortality rates among U.S. women under 40 have leveled off after more than two decades of declines and may now be rising, a new study suggests.

Researchers examined data from the National Center for Health Statistics on breast cancer mortality rates among women 20 to 79 years old from 1969 to 2017, looking separately for trends within each 10-year age group. Overall breast cancer mortality rates declined by 1.5% to 3.4% per year from 1989 to 2010 for women in each age group.

After 2010, however, trends looked different for younger and older women in the study. Among those aged 40 to 79 years, mortality rates kept dropping by 1.2% to 2.2% annually, but declines slowed for women aged 70-79 and stopped for those under 40.

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For the youngest women in the study, aged 20 to 29 years, breast cancer mortality rates had nonsignificant annual increases of 2.8% a year after 2010, while women 30 to 39 years had nonsignificant annual increases of 0.3%.

"One major contributing factor … is that the incidence rates of distant-stage (metastatic) breast cancers in women 20-39 years old have increased by more than 4% per year since the year 2000," said lead study author Edward Hendrick, a clinical professor at the University of Colorado School of Medicine, Anschutz Medical Campus, in Aurora.

"Over the same period, distant-stage breast cancers have increased by a much lower rate of 1.2% per year in women 40-69," Hendrick said by email. "We don't know the reasons behind this rapid increase in these killing cancers in younger women."

Beyond the rise in metastatic cancer, an analysis by race and ethnicity found rising breast cancer deaths among white women may be driving the increased mortality rates in women under 40.

Mortality for women under 40 decreased significantly from 1990 through 2017 among Black, Asian, Native American, and Hispanic women, researchers report in Radiology. But mortality rates for white women rose by an average of 1.6% per year during the study period.

One limitation of the study is that researchers lacked data on individual tumor grade, node status, and receptor status, the authors note. It's also not clear from the data whether cancers were detected via screening, clinical exam, or self-exams.

It's possible that mortality rates kept declining for women over 40 because they are more likely to undergo routine screening mammography, which has been proven to reduce mortality from breast cancer, said Dr. Catherine Tuite, an associate professor of radiology and section chief for breast imaging at Fox Chase Cancer Center in Philadelphia.

"The national guidelines for treatment of newly diagnosed breast cancers are the same regardless of age at diagnosis, so differences in treatment of older or younger women do not explain the differences in mortality," Dr. Tuite, who wasn't involved in the study, said by email.

The current study adds to evidence demonstrating the mortality benefits of screening mammography in average-risk women beginning at age 40 and continuing yearly until life expectancy is less than 5 to 10 years, Dr. Tuite said.

"In addition, I believe that this data emphasizes the recommendation that all women should undergo formal risk assessment for breast cancer by age 30," Dr. Tuite said. "This may help identify women who are at higher than average risk for breast cancer so that they may benefit from earlier screening as appropriate."

—Lisa Rapaport

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