With rising cases of breast cancer among young women, researchers have made a surprising discovery: the risk isn't the same across all U.S. states. In fact, your risk may depend on where you live.

A recent study published in Cancer Causes & Control examined how breast cancer risks in the last two decades vary across different states, regions, and areas, while also considering racial and ethnic differences.

"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. Our findings can more accurately inform whether exposures that vary in prevalence across the U.S. also contribute to breast cancer risk in younger women," said lead researcher Rebecca Kehm in a news release.

Researchers found that breast cancer in women below the age of 40 has increased by more than 0.50 percent in 21 U.S. states. The study identified 12 states with a significant rise in risk: Illinois, Minnesota, Wisconsin, Massachusetts, New Hampshire, New York, Pennsylvania, Delaware, Louisiana, California, Colorado, and Oregon. The rest of the states either showed a stable rate or a decreasing trend between 2001 to 2020.

Compared to the five states with the highest breast cancer rates (Maryland, New York, New Jersey, Hawaii, and Connecticut), the five states with the lowest rates (Idaho, North Dakota, Arizona, Utah, and Wyoming), had a 32% lower incidence of breast cancer.

Region-wise analysis shows that the Western region had the highest rate of increase in breast cancer cases among women under 40. The Northeast had the highest absolute rate, while the South was the only region where breast cancer rates in women under 40 did not rise.

The trend also varied by race, with non-Hispanic Black women facing the highest risk of early-onset breast cancer. Hispanic women had the lowest rates of early-onset breast cancer across all regions. Meanwhile, Non-Hispanic White women were the only group to have a statistically significant increase in early-onset breast cancer incidence across all four U.S. regions.

Based on these findings, researchers recommend that doctors consider the location also as a factor while evaluating a woman's risk of breast cancer incidence.

"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," Kehm said.

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