Women with breast cancer have more aggressive disease and lower survival rates if they are overweight or obese, according to findings published in the March 15 issue of Clinical Cancer Research, a journal of the American Association for Cancer Research.

“The more obese a patient is, the more aggressive the disease,” said Massimo Cristofanilli, MD, associate professor of medicine in the Department of Breast Medical Oncology at The University of Texas M.D. Anderson Cancer Center. “We are learning that the fat tissue may increase inflammation that leads to more aggressive disease.”

Cristofanilli and colleagues observed 606 women with locally advanced breast cancer. These women were classified by body mass index into the following three groups: normal/underweight (24.9 or below), overweight (at least 25 but less than 30) or obese (more than 30). Body mass index is calculated by dividing a person’s weight by their height.

At five years, overall survival was 56.8 percent among obese women, 56.3 percent among overweight women and 67.4 percent among normal weight women. The 10-year survival rate was 42.7 percent among obese women, 41.8 percent among overweight women and 56.5 percent among normal weight women.

The rate of inflammatory breast cancer, previously shown to have worse outcomes than non-inflammatory breast cancer, among obese women was 45 percent compared with 30 percent in overweight women and only 15 percent in women considered normal weight, researchers found.

Risk of breast cancer recurrence was also higher in obese or overweight women. By five years, 50.8 percent of obese women reported a recurrence compared with 38.5 percent of normal weight women. By 10 years, the rate of recurrence was 58 percent among obese women and 45.4 percent among normal weight women.

“Obesity goes far beyond just how a person looks or any physical strain from carrying around extra weight. Particular attention should be paid to our overweight patients,” Cristofanilli said.

Cristofanilli said physicians need to pay close attention to breast cancer patients because commonly used drugs, such as tamoxifen, tend to increase weight gain during treatment.

“We have actually become quite good at managing acute side effects such as nausea in our chemotherapy patients and it goes away within a couple of days,” Cristofanilli said.

“Following the nausea, our patients tend to overeat, which further increases their risk of weight gain. We need to implement lifestyle modifications interventions and develop better methods to follow these patients closely.”