Abstract P6-07-39: Prognostic Value of Body Mass Index in Japanese Breast Cancer Patients: A Collaborative Study by the Kobe Breast Cancer Oncology Group and Hokkaido Cancer Center

Background: Many recent clinical trials conducted in Western populations suggest that obesity is a prognostic factor after primary treatment in postmenopausal breast cancer patients. However, the incidence of obesity differs substantially between Asian and Western breast cancer patients. Moreover, few studies have reported the relationship between body mass index (BMI) and postsurgical prognosis in Asian breast cancer patients. A previous retrospective analysis of Japanese populations revealed that obesity might be a prognostic risk factor in Japanese breast cancer patients. Methods: We retrospectively analyzed BMI and clinical outcomes after primary treatment in Japanese breast cancer patients of Hanshin and Hokkaido areas. We reviewed the clinical data (height, weight, BMI, estrogen receptor [ER] status, progesterone receptor status [PgR], human epidermal growth factor receptor 2 [HER2] status, and outcome) of 1,222 primary breast cancer patients with clinical stage I-III disease who were operated on between Jan 2004 and Dec 2005 at Kobe Breast Cancer Oncology Group (KBCOG) and Hokkaido Cancer Center (median follow-up period, 74 months). The patients were categorized into 4 groups: underweight (BMI, 2 ), normal (18.5–24.9 kg/m 2 ), overweight (25–29.9 kg/m 2 ), and obesity (>30.0 kg/m 2 ). Patient characteristics, excluding age and menopausal status, were well-balanced across groups. The correlations of BMI with disease-free survival (DFS) and overall survival (OS) were analyzed using the Cox hazards model. Results: The normal, underweight, overweight, and obesity groups contained 832 (68.1%), 92 (7.5%), 253 (20.7%), and 45 (3.7%) patients, respectively. Breast cancer recurred in 184 patients (15.0%); 75 patients died due to breast cancer recurrence, 29 died of other diseases, and 6 died of unknown causes. The univariate hazard ratio (HR) values for disease-free survival and overall survival in the overweight group were significantly lower than those in the normal group. However, there were no statistical significant differences among four groups by the multivariate analysis. We added subgroup analysis with classifications by ER and PgR status to speculate the cause for these unexpected results. Although there were no statistically significant differences, HRs for DFS and OS in the obesity group were higher than those in the normal group among ER− and/or PgR-positive patients. However, HRs for DFS and OS tended to be higher in the underweight groups and lower in the overweight groups in ER− and PgR-negative populations. Conclusions: The incidence of obesity in the Japanese population is much lower than that in the Western population. Although results of this study were slightly different from recent findings, obesity might be a risk factor for DFS and OS in ER-positive Japanese breast cancer patients, similar to that in Western countries. In underweight patients, ER− and PgR-negative status might indicate poor prognosis. However, this study was a retrospective analysis of a limited, heterogeneous patient group. A large-scale cohort study in the Japanese population is, therefore, recommended. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-07-39.