The researchers presented the data today at the 34th annual San Antonio Breast Cancer Symposium, jointly sponsored by Baylor College of Medicine, the American Association of Cancer Research, and the Cancer Therapy and Research Center at the University of Texas Health Science Center in San Antonio.
“There is a lot of evidence that suggests obesity puts a breast cancer patient at risk for worse survival outcomes,” said Dr. Sao Jiralerspong, assistant professor in the Smith Breast Center and lead author on the study. “But we do not yet know how obesity affects different treatment groups, so we specifically examined the link between weight and outcomes in the different adjuvant therapy groups.”
Whole body treatment
Adjuvant therapy is treatment given following the initial local therapy with surgery. Its purpose is to provide whole-body treatment to keep the cancer from returning. Adjuvant therapy can include chemotherapy, endocrine (hormone) therapy, or targeted therapy.
Jiralerspong and team retrospectively studied a large group (4,368) of early-stage (1, 2 and 3) patients from the Baylor Breast Center Tumor Bank treated from 1970–1995.
The patients were separated into three weight classes or BMI (body mass index) groups – normal/underweight (BMI less than 25); overweight (BMI 25 to 30); or obese (BMI greater than or equal to 30).
The patients were also divided into four different treatment groups – no adjuvant therapy; chemotherapy; endocrine therapy and both chemotherapy and endocrine therapy.
For the group overall, survival outcomes were significantly worse in the obese patients as compared with normal weight patients, the researchers found.
Obesity may offset chemo benefits
“When we compared the different treatment groups, being obese was associated with worse survival outcomes among patients who received adjuvant chemotherapy,” said Jiralerspong. “The magnitude of this effect was large enough that, for some patients, obesity may have offset the benefits of chemotherapy.”
One surprising finding – in the patients who received adjuvant endocrine therapy, being overweight was associated with better survival rates when compared with normal weight patients.
More research in this area is critical, to further define the effects of obesity on breast cancer in different patient and treatment subgroups, Jiralerspong said.
“More and more evidence, such as our study, is confirming the association between obesity and worse breast cancer outcomes. Now, we need to look at what obesity does to the body to confer that risk. And whether we can develop targeted therapies to counteract the negative effects of obesity.”
In addition to Jiralerspong, BCM collaborators on the study included Dr. Tao Wang; Dr. Mothaffar Rimawi; Dr. Julie Nangia; Dr. Rachel Schiff; Carol Chenault; Dr. Kent Osborne; and Dr. Susan Hilsenbeck. Dr. Sharon Giordano at the University of Texas M.D. Anderson Cancer Center and Dr. Michael Pollak at McGill University in Montreal, Canada also collaborated on the study.
Funding from the study came from the Lester and Sue Smith Breast Center at BCM.