February 19, 2025-- Breast cancer incidence trends in U.S. women under 40 vary by geography and supports incorporating location information with established risk factors into risk prediction, improving the ability to identify groups of younger women at higher risk for early-onset breast cancer, according to a new study at Columbia University Mailman School of Public Health. This study comprehensively examined trends across different states, regions, metropolitan versus non-metropolitan areas and by racial and ethnic groups. It also is one of the first to incorporate registry data from all 50 states to examine age-specific breast cancer trends. The findings are published in the journal Cancer Causes & Control .
"Breast cancer incidence is increasing in U.S. women under 40, but until now, it was unknown if incidence trends varied by U.S. geographic region," said Rebecca Kehm, PhD, assistant professor of Epidemiology at Columbia Mailman School, and first author. "Our findings can more accurately inform whether exposures that vary in prevalence across the U.S. also contributes to breast cancer risk in younger women."
Using the U.S. Cancer Statistics database, the researchers analyzed age-adjusted breast cancer-incidence rates from 2001 to 2020 in women aged 25-39. They calculated the average annual percent change using statistical regression formulas and performed age-distribution analyses.
"Two-thirds of all cancers identified both in the U.S. and globally are diagnosed in women," said Mary Beth Terry, PhD, professor of Epidemiology at Columbia Mailman School of Public Health, and senior author of the study.
From 2001 to 2020, breast cancer incidence in women under 40 increased by more than 0.50 percent per year in 21 states, while remaining stable or decreasing in the other states. Incidence was 32 percent higher in the five states with the highest rates compared to the five states with the lowest rates. The Western region had the highest rate of increase from 2001 to 2020; the Northeast had the highest absolute rate among women under 40 and experienced a significant increase over time The South was the only region where breast cancer under 40 did not increase from 2001 to 2020.
The overall incidence of early-onset breast cancer ranged from 28.6 per 100,000 in Wyoming to 41 cases per 100,000 people in Connecticut. The five states with the highest early-onset incidence from 2001 to 2020 were Maryland, New York, New Jersey, Hawaii, and Connecticut. Hispanic women had the lowest early-onset frequency rates in all regions, ranging from 26 per 100,000 in the Midwest to 32.6 per 100,000 in the Northeast.
Non-Hispanic White women were the only group to experience a statistically significant increase in early-onset breast cancer incidence across all four regions of the U.S. Non-Hispanic Black women had the highest incidence of early-onset breast cancer. This was true across the regions of the country.
The authors note the importance of investigating other risk factors including alcohol consumption, an established risk factor for breast cancer and which is known to vary across states and also be influenced by state alcohol policies.
"The increase in incidence we are seeing is alarming and cannot be explained by genetic factors, alone which evolve over much longer periods nor by changes in screening practices given that women under 40 years are below the recommended age for routine mammography screening," noted Kehm.
"While the causes behind the rising incidence of early onset breast cancer are not yet fully understood, studying how trends vary across different population subgroups can offer valuable insights and help generate hypotheses for future research," said Professor Terry. "We also are able to gain an understanding into the increase in breast cancer incidence among women who are not currently recommended for routine screening."
Co-authors are Josephine Daaboul, Columbia Mailman School of Public Health and Fielding School of Public Health, University of California Los Angeles; and Parisa Tehranifar, Columbia Mailman School of Public Health.
The study was supported by the National Cancer Institute (R00CA263024).
Columbia University Mailman School of Public Health
