Obesity Raises Breast Cancer Death Rate By a Third

Yan Ling Zhong, Jen Brodeur
Jen Brodeur, right, Tufts Medical Center mammographer, prepares Yan Ling Zhong of Boston for a digital mammogram in 2010. Bizuayehu Tesfaye / AP

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Younger women who are obese have a 34 percent higher risk of dying from their breast cancer, a new study finds.

Doctors have long known that being overweight or obese raises a woman’s risk of developing breast cancer, and they know it’s not especially good for women who have it, either. What’s not been clear is just how harmful it is, and whether a woman’s age or the type of cancer she has matters.

The new study, which will be presented next month at the annual meeting of the American Society of Clinical Oncology, found that obesity is only significantly dangerous for women who get breast cancer before menopause and who have the type that’s fed by the hormone estrogen.

Hongchao Pan and colleagues at Britain’s University of Oxford looked at data on 80,000 women with breast cancer. They found that for the women who were already past menopause, and those who had so-called hormone-negative breast cancer, being obese didn’t matter.

But it did for the younger women with hormone-positive breast cancer — the most common kind.

“Despite everyone knowing the truth of this, the levels of overweight and obesity in the U.S. continue to climb,” said ASCO president Dr. Clifford Hudis. “Knowing that it is a negative health factor in so many domains is not yet an effective way of changing behavior.”

More than a third of American women are obese and another third are overweight.

Fat cells produce estrogen and this may be a factor. Breast cancer is the second-leading cancer killer among U.S. women, after lung cancer. Every year it's diagnosed in 200,000 women and a few men, and kills around 40,000.