According to Kerlikowske, adding strength to the idea that the increased estrogen in heavy women is fueling the tumor is the fact that the rate of tumors called "estrogen receptor-positive" (which are spurred on by estrogen) increased across the various weight groups, while ER-negative tumors did not.
Kerlikowske's team used the standard definitions of healthy weight, overweight, and obesity. For instance, a 5-foot, four-inch woman who weighs from 107 to 145 was considered at a healthy weight. The same woman weighing 146 pounds or more was considered overweight, and a weight of 175 pounds or more was considered obese.
About two-thirds of American adults are now either overweight or obese, according to recent government statistics.
Of the study, Kerlikowske said: "It's very representative. It's from mammography registries across the U.S."
The research provides valuable new information on basic biology and risk factors for breast cancer, said mammography researcher Dr. Joann Elmore, professor of medicine and adjunct professor of epidemiology at Harborview Medical Center in Seattle. "They basically found that there are biological effects of obesity, and this can influence breast cancer development or progression."
The study results, Elmore said, should inspire women who are above their healthy weight to shed some pounds. While many risk factors -- such as increasing age, being female, or having genetic mutations that raise breast cancer risk -- are not changeable, losing weight remains under a woman's control, she said.
Kerlikowske agreed. "Here is a risk factor to modify," she said.
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