Women younger than 50 who are obese and have a common form of breast cancer have a higher risk of dying from the disease than women with the cancer who are normal weight, researchers said.
Being obese was associated with a 34 percent increased chance of breast cancer death in pre-menopausal women with estrogen receptor-positive disease, which responds to hormone treatment, an analysis of 70 clinical trials found. The study, released yesterday, will be presented at the American Society of Clinical Oncology meeting beginning May 30 in Chicago.
The research is among the latest to tie obesity to cancer risk and the largest to examine weight’s role in the prognosis of estrogen-receptor positive breast malignancy and menopausal status, the authors said. Obesity is associated with increased dangers of other cancers including esophagus, endometrium, colon, kidney, pancreas, thyroid and gallbladder, according to the National Cancer Institute.
“This study is part of the growing body of evidence showing that patients who are obese generally fare worse with cancer –- in this case, younger women with breast cancer,” Clifford Hudis, president of the cancer doctors’ group, said in a statement. “With some two-thirds of our nation’s adult population now obese or overweight, there’s simply no avoiding obesity as a complicating factor in cancer care.”
Breast cancer is the most diagnosed cancer among U.S. women, according to the Centers for Disease Control and Prevention. Two-thirds of all breast tumors are fed by estrogen, according to the National Institutes of Health. More than 230,000 women in the U.S. will be diagnosed with breast cancer this year and 40,000 will die.
The study’s results showed no association between weight and death in post-menopausal women with estrogen receptor-positive disease, a surprise finding because obesity increases blood estrogen levels in older women, said lead study author Hongchao Pan.
“This is exactly the opposite of what we expected,” Pan, a senior research fellow at the University of Oxford in the U.K., said in a telephone interview. “We know the effect is definite and real. We don’t know the mechanisms that underlie the association at the moment.”
Researchers in the study looked at 80,000 women in 70 clinical trials. Of those, 20,000 were pre-menopausal with ER-positive disease, 40,000 had ER-positive disease and were post-menopausal and 20,000 were pre-menopausal with ER-negative disease.
They found that both overweight and obese pre-menopausal women had a higher risk of dying from ER-positive breast cancer compared with women who were normal weight.
78 Million Obese
About 78 million adults, or about one-third of the U.S. population, are obese as are 17 percent of children and teenagers younger than 19, according to the CDC.
Body mass index, or BMI, is a measure of weight and height, with a 5-foot 4-inch woman weighing 175 pounds having a BMI of 30. A BMI of 30 or more is considered obese, while a BMI of 25 to 29.9 is considered overweight, according to the NIH.
The researchers found no association between body mass index and risk of dying in pre-menopausal women with ER-negative disease, Pan said.