Extra pounds—even within the overweight but not obese range—are linked to a higher risk of recurrence of the most common type of breast cancer despite optimal cancer treatment, according to a new study published early online in CANCER, a peer-reviewed journal of the American Cancer Society. The study's results suggest that extra body fat causes hormonal changes and inflammation that may drive some cases of breast cancer to spread and recur despite treatment.
Women who are obese when they are diagnosed with breast cancer have an increased risk of dying prematurely compared with women of normal weight. In this new study, Joseph Sparano, MD, of the Albert Einstein College of Medicine's Montefiore Medical Center, in Bronx, NY, and his colleagues across the US cancer cooperative groups compared the health outcomes of obese and overweight patients with others in a large group of women with stage I-III breast cancer who had participated in three National Cancer Institute–sponsored treatment trials led by the Eastern Cooperative Oncology Group (now part of the ECOG-ACRIN Cancer Research Group). All of the trials (E1199, E5188, and E3189) required participants to have normal heart, kidney, liver, and bone marrow function, thereby excluding patients with other significant health issues. As a result, researchers were able to disentangle the influence of obesity from other factors affecting cancer recurrence and survival.
The researchers found that increasing body mass index—a measure of the body's fat content—significantly increased women's risk of cancer recurrence and death, despite optimal treatment including chemotherapy and hormonal therapy. There was a stepwise relationship between increasing body mass index and poor outcomes only in women with hormone receptor–positive breast cancer, the most common type of breast cancer that accounts for approximately two-thirds of all breast cancer cases in the United States and worldwide.
"We found that obesity at diagnosis of breast cancer is associated with about a 30 percent higher risk of recurrence and a nearly 50 percent higher risk of death despite optimal treatment," said Dr. Sparano. "Treatment strategies aimed at interfering with hormonal changes and inflammation caused by obesity may help reduce the risk of recurrence," he added.