Abstract PD2-1: Body mass index at diagnosis and breast cancer survival prognosis among clinical trial populations: Results from NSABP B-30, B-31, B-34, and B-38

Background: Body mass index (BMI) has been associated with the risk of developing breast cancer and with breast cancer outcomes including recurrence and death. However, results from previous studies have been limited in that few have been conducted in clinical trial settings where treatment regimens and outcome measurements are consistently evaluated and well documented. There is also limited data evaluating how patient characteristics, disease characteristics, and treatment may alter the association of BMI with breast cancer risk and breast cancer outcomes. Methods: To investigate the relationship between BMI at diagnosis and survival in populations of women with different types of breast cancer, we assessed data from 15,538 breast cancer patients who participated in four NSABP protocols (B-30, B-31, B-34 and B-38). Protocol B-34 was conducted in a general population of early-stage breast cancer patients (N = 3,311); B-30 and B-38 included patients with node-positive breast cancer (N = 5,265 and 4,860, respectively); and B-31comprised women with node-positive breast tumors that overexpress the HER2 protein (N = 2,102). For each trial, BMI at the time of diagnosis was categorized into: <25; 25.0-29.9; and ≥30. Cox proportional hazards regression was used to calculate unadjusted and adjusted hazards ratios (HRs) for risk of death. Explanatory variables included in the multivariable models were treatment, age, menopausal status, estrogen receptor (ER) status, number of positive nodes, tumor size, and tumor grade, when available. As it was of a particular interest, we conducted separate analyses among ER-positive and ER-negative breast cancers to assess effects of BMI by tumor receptor status. Results: Among participants in B-30, we found a significant relationship between increased BMI and survival. Compared with BMI <25, adjusted HRs were 1.04 for BMI 25-29.9 and 1.18 for BMI ≥30 (p = 0.02). However, for the other three trials there was no statistically significant trend across BMI categories. The adjusted HRs for overweight and obese women were 0.83 and 0.94 (p = 0.58) in B-31; 0.93 and 1.03 (p = 0.76) in B-34; and 1.02 and 1.11 (p = 0.26) in B-38. Separate analyses by ER-status showed that the significant relationship found in B-30 was present in those with ER-positive breast cancers (p = 0.002) but not ER-negative breast cancers (p = 0.88). No significant results were found for either ER-negative or ER-positive breast cancers for the remaining three trials. When assessing ER-positive tumors, the p-values were 0.96, 0.88, and 0.20 for B-31, B-34, and B-38, respectively. When assessing ER-negative tumors, the p-values were 0.52, 0.37, and 0.92 for B-31, B-34, and B-38, respectively. Conclusions: In our investigation among breast cancer clinical trial participants, we did not find a consistent relationship between BMI at diagnosis and survival. An association was evident in only one of the four trial populations. Furthermore, the significant relationship found in B-30 participants was evident only in those with ER-positive breast cancer. Support: NCI-U10-CA-12027, U10-CA-37377, U10-CA-69974, U10-CA-69651; Aventis Pharmaceuticals; Genentech Inc; Schering Oy; Amgen Inc; Eli Lilly & Company. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr PD2-1.