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In a nutshell
- Early-onset breast cancer rates in women under 40 vary significantly by location in the U.S., with a 32% difference between the five highest-rate states (Maryland, New York, New Jersey, Hawaii, Connecticut) and the five lowest-rate states
- While Western states had the lowest overall rates, they showed the fastest increase (0.76% annually). The South was the only region where rates remained stable from 2001-2020
- Geographic differences in early breast cancer rates are comparable to variations seen with genetic risk factors, suggesting where young women live could be as important as their genetic predisposition
NEW YORK — A new nationwide study suggests that a young woman’s location may play a significant role in breast cancer risk, with geographic differences comparable in magnitude to genetic risk scores. The research, examining data from all 50 states over two decades, shows that early breast cancer rates in women under 40 vary significantly depending on where they live.
“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,” says Rebecca Kehm, PhD, assistant professor of Epidemiology at Columbia Mailman School and lead author of the study, in a statement.
The numbers tell a striking story. From 2001 to 2020, breast cancer rates in young women increased by more than half a percent each year in 21 states. However, only 12 of these states showed statistically significant increases. The five states with the highest early breast cancer rates had 32% more cases than the five states with the lowest rates—a difference comparable to established genetic risk measures.
Maryland, New York, New Jersey, Hawaii, and Connecticut had the highest early breast cancer rates. At the other end of the spectrum, Idaho, North Dakota, Arizona, Utah, and Wyoming had the lowest rates. Connecticut had about 40.8 cases per 100,000, while Wyoming reported 28.6 cases per 100,000.
Regional patterns emerged as well. The Western states, despite having the lowest overall rates, showed the fastest increase at about 0.76% per year. The Northeast maintained the highest total numbers and continued to see significant growth. Meanwhile, the South stood out as the only region where early breast cancer rates remained stable rather than rising between 2001 and 2020.
The study also found clear differences between urban and rural areas. Cities across all regions saw increases in early breast cancer rates. However, only the Northeast and West showed significant increases in their rural areas, suggesting that urban-rural differences play a role in these trends.
Race and ethnicity factored significantly into the geographic picture. Non-Hispanic Black women consistently showed the highest early breast cancer rates across all regions, ranging from 39.3 cases per 100,000 in the West to 44.3 per 100,000 in the South. Hispanic women had the lowest rates, varying from 25.8 per 100,000 in the Midwest to 32.6 per 100,000 in the Northeast.
“The increase in incidence we are seeing is alarming and cannot be explained by genetic factors alone,” notes Kehm. She also points out that these trends can’t be attributed to changes in screening practices, since women under 40 aren’t typically recommended for routine mammograms.
So what might explain these geographic differences? The researchers suggest several possibilities, including environmental factors like air pollution, differences in behaviors such as breastfeeding and alcohol consumption—an established breast cancer risk factor that varies by state policy—access to healthcare, and state-level policies, such as paid leave for new mothers.
“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,” says Mary Beth Terry, PhD, the study’s senior author.
Paper Summary
Methodology
Researchers utilized the US Cancer Statistics database, analyzing age-adjusted breast cancer incidence rates for women aged 25-39 from 2001 to 2020. They employed statistical techniques including joinpoint regression to calculate average annual percent changes and conducted age-period-cohort analyses to understand how trends varied across different age groups, time periods, and birth cohorts. The study examined data across all 50 states, though three states (North Dakota, Vermont, and Wyoming) were excluded from some analyses due to small case counts.
Results
The analysis revealed that early-onset breast cancer increased by 0.42% annually nationwide from 2001 to 2020. Twenty-one states showed increases greater than 0.50% annually, though only twelve reached statistical significance. The Western region showed the highest rate of increase (0.76%), while the South remained stable. Metropolitan areas consistently showed increases across all regions, while rural areas varied significantly. The study found substantial racial and ethnic disparities, with Non-Hispanic Black women showing the highest rates across all regions.
Limitations
The research was constrained by the timeframe of available data (only back to 2001) and couldn’t assess trends at more detailed geographic levels like counties or cities. Small population sizes in certain areas may have limited the ability to identify significant trends, particularly in rural regions and among certain racial/ethnic groups. The database also lacked information about risk factors, preventing direct analysis of what might be driving these geographic differences.
Discussion and Takeaways
The findings suggest that incorporating geographic factors into breast cancer risk assessment could improve identification of high-risk younger women. The substantial variation in rates between states (32% difference between highest and lowest) indicates that place-based factors may be as important as genetic predisposition. The study highlights the need for targeted interventions and policies that address both regional and demographic disparities in breast cancer risk.
Funding and Disclosures
The research was supported by the National Cancer Institute (R00CA263024) and conducted by researchers from Columbia University and the University of California Los Angeles. The authors declared no competing interests.
Publication Information
The study, titled “Geographic differences in early-onset breast cancer incidence trends in the USA, 2001-2020, is it time for a geographic risk score?” was published in Cancer Causes & Control in February 2025. The research was conducted by Rebecca D. Kehm, Josephine M. Daaboul, Parisa Tehranifar, and Mary Beth Terry.
