(CNN) Scientists know obese people have an increased risk of getting several types of cancer. But a new study suggests being obese also increases the chance that some patients’ cancers will come back, and increases the likelihood that those patients will die from cancer.
The study was released in advance of the 2014 American Society of Clinical Oncology annual meeting, which begins on May 30.
Researchers looked at 80,000 patients in 70 early breast cancer trials and analyzed their body mass index, estrogen receptor, menopause status, cancer recurrence and their prognosis.
They compared women with higher BMIs (over 30) to those with normal BMIs (20-25) over a 10-year period. They found for younger, pre-menopausal women who have early breast cancer, obesity appears to be strongly linked to worse outcomes, including death.
Specifically, women with BMIs over 30 had a 21.5% chance of dying while women with average BMIs had 16.6% chance of dying. This only applied to women with hormone-receptor-positive breast cancer. Researchers found no apparent effect of obesity in women with estrogen-receptor-negative cancer, according to lead study author Hongchao Pan, a researcher at the University of Oxford.
“The findings from this study support current recommendations that women maintain a healthy weight following a diagnosis of breast cancer,” Dr. Ruth O’Regan, a Winship Cancer Center oncologist, told CNN in an email.
This study was surprising in its finding about pre-menopausal women, says Susan Neuhausen, a breast cancer researcher at the City of Hope in Duarte, California. She says it “provides information that clinicians may want to more closely monitor pre-menopausal women who are obese at diagnosis.”
Neuhausen said it’s not clear why this is true in just pre-menopausal women.
Obesity is known to cause inflammation in the body, said Dr. Clifford A. Hudis, president of the American Society of Clinical Oncology. This inflammation may activate CYP19 — the aromatase gene, which is responsible for estrogen conversion. And estrogen is known to fuel cancer growth in hormone-receptor-positive breast cancer.
Hudis said it’s remarkable that only about 4% of people doubt the connection between smoking and cancer, yet just 10% of people understand the link between obesity and cancer. “No matter how we look at it, obesity is looking to replace tobacco as the overall leading factor leading to cancer.”