new data suggest.
Obesity is a well-known risk factor for breast cancer in postmenopausal women and has been associated with adverse prognosis, said Senna W.M. Lammers, MD, of Maastricht (the Netherlands) University during a presentation at the European Society for Medical Oncology (ESMO) Breast Cancer annual congress. In addition, some studies suggest that patients with higher body mass index (BMI) experience reduced benefits from endocrine therapy, she said.
Dr. Lammers and colleagues conducted a study to determine the prognostic and predictive effect of BMI on disease-free survival in postmenopausal women with hormone receptor–positive (HR+) breast cancer who were treated with extended endocrine therapy.
The study population included participants in the randomized, phase III DATA trial, which evaluated the use of 6 years vs. 3 years of anastrozole in postmenopausal women with HR+ breast cancer who were disease-free after 2-3 years of adjuvant tamoxifen therapy.
Patients were categorized based on BMI as having normal weight (18.5-24.9 kg/m2), overweight (25-29.9 kg/m2), or obese (30 kg/m2 or higher). The primary outcome was disease-free survival (DFS); the median follow-up period was 13.1 years.
DFS for patients with normal weight, overweight, and obesity was 66.2%, 59.5%, and 52.4%, with a P value of less than .001 for the trend, Dr. Lammers said. “These results were confirmed in multivariable analysis,” she said. Overall, patients with overweight and obesity had a worse DFS when compared with patients with normal weight (hazard ratio, 1.16; P = .10, for patients with overweight and HR, 1.26; P = .03 for patients with obesity).
“Next, we aimed to determine whether the prognostic effect of BMI differed by age,” Dr. Lammers said.
In women younger than 60 years, overweight and obesity were significantly associated with worse DFS (HR, 1.29; P = .05 and HR 1.83, P less than .001, respectively). However, this effect was not observed in women aged 60 years and older.
The researchers also examined the treatment effect of extended anastrozole on adapted DFS by weight, and found no significant differences among patients with normal weight, overweight, and obesity (HR, 1.00; HR, 0.74; and HR, 0.97, respectively), said Dr. Lammers.
In the question and answer session, Dr. Lammers was asked about possible explanations for the difference in DFS by age. Potential explanations include possible survival bias “as only the healthier [patients with obesity] survive to old age,” she said. Other potential explanations are biological, such as the potentially higher levels of bone density in older [patients with obesity], she said.
When asked about additional clinical implications, Dr. Lammers emphasized the importance of maintaining a healthy BMI for breast cancer patients of all ages. Other research areas might involve the use of lifestyle interventions, although these are challenging to implement, she noted.