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.
Source : https://studyfinds.org/breast-cancer-rates-young-women-location/
