Why More Young Women Are Getting Breast Cancer

The number of young women being diagnosed with breast cancer is rising—especially among those in their 20s, 30s and early 40s. And this isn’t just a random trend. According to an article from Washington University School of Medicine, researchers have found a sharp increase in estrogen-driven breast cancers in younger women over the last decade.

This type of breast cancer, called estrogen receptor positive (or ER+), grows in response to estrogen. So the big question is: why are younger women seeing more of it now?

One factor is that girls are starting their periods earlier than in past generations. That means more years of estrogen exposure, and according to WashU’s research, even getting your period one year earlier can raise your breast cancer risk by nearly 10%.

Another reason? People are having fewer children, and they’re waiting longer to have them. Having your first baby before 30 and having multiple pregnancies can help lower the risk of ER+ breast cancer. But nationwide, those patterns have shifted—and it may be playing a role in the increase.

Researchers, including Dr. Adetunji Toriola, are also studying how dense breast tissue, environmental chemicals and lifestyle changes are shaping breast cancer risk. Drinking habits, for example, look different than they used to. Younger women are more likely to binge drink, and alcohol can fuel ER+ tumor growth. Add in fast weight gain, sedentary routines and ultra-processed diets, and there’s a perfect storm forming before age 40.

The bottom line, according to WashU’s findings: breast cancer prevention shouldn’t wait until your first mammogram. What you do now—how you eat, move, drink and track your health—can matter more than you think.