Genes for Weight Gain Tied to Breast Cancer Risk

New research suggests that the connection between body weight and breast cancer survival may be more than just a lifestyle question. According to a study published in JAMA Network Open, women who have a genetic predisposition to carry excess body weight faced a higher risk of death after a breast cancer diagnosis than those without that genetic pattern.  

The study followed more than 4,000 postmenopausal women in the United States who had been diagnosed with nonmetastatic breast cancer. Researchers calculated a “polygenic score” for each woman, which is a way of estimating inherited risk for having a higher body mass index based on many genetic markers. Women whose scores were in the highest third had about a 15 percent greater risk of dying from any cause over the years after their diagnosis, compared with women whose scores were in the lowest third.  

That doesn’t mean genes are destiny, but it does highlight how biology and lifestyle interact to shape long-term health. According to the study, women with a higher genetic propensity for weight gain needed more physical activity to achieve the same survival benefit as others. For example, survivors in the highest genetic risk group had to walk about an extra 15 minutes each day to bring their mortality risk down to a level similar to those with lower genetic risk.  

Scientists have long known that excess body weight is linked with poorer outcomes after breast cancer, but this research adds a genetic layer to that story. It shows that some women may inherit a stronger tendency toward higher body mass, and that inherited risk may influence their prognosis after cancer. The findings suggest that awareness of genetic predisposition could help shape personalized lifestyle recommendations for survivors, especially when it comes to physical activity and weight management.  

What’s especially promising is that the study points to action, not inevitability. Walking more each week provided measurable benefit, even for women with higher genetic risk. That means tailored guidance on physical activity and weight control could become part of survivorship care plans, giving women tools to support their long‑term health after breast cancer.  

As research continues, understanding how genetics interacts with lifestyle and environment will be key to creating more personalized and hopeful approaches to survivorship.