Abstract P1-07-13: Obesity is associated with poor prognosis of Japanese breast cancer, especially in ER positive/HER2 negative subtype, which tendency is prominent

Introduction : Body mass index (BMI) is defined as a poor prognostic factor in breast cancer patients in western countries. Since the percentage of the overweight differs between Asian and western breast cancer patients, we do not know if breast cancer prognosis in Asia is related to obesity, the same as in western countries. Therefore, we have investigated the association between BMI and the prognosis of Japanese breast cancer patients. Patients and Methods : This study is a retrospective analysis of the 1,924 primary Japanese female breast cancer patients with clinical stage I through III disease to have undergone surgery between January 2004 and December 2013 at the Hokkaido Cancer Center. The data of BMI were at the time of diagnosis, and stratified into 2 groups as non-Obese (BMI 2 ), Obese (BMI ≥ 25 kg/m 2 ). The overall survival (OS) and disease-free survival (DFS) were compared between two BMI groups using the Kaplan-Meier method and Cox hazards model. Results : The number of non-Obese group was 1,353 (70.3%) and Obese group was 571 (29.7%) of the 1,924 patients. Six hundred and thirty two patients were in premenopausal (32.8%), 1,289 were in postmenopausal (67.0%) and 3 were unknown. The median follow-up period was 73 months. Breast cancer recurred in 239 patients (12.2%), and 204 patients died. There were 110 cases of breast cancer-related death, 48 cases of non-breast cancer death, and 46 cases of unknown as the cause of death. Patients in Obese group had shown significantly poorer OS (adjusted hazard ratio (HR) = 1.68, 95% confidence interval (CI) = 0.45 to 0.79) and DFS (HR = 1.46, 95% CI = 1.16 to 1.82). As investigating by subtype analysis, a high BMI in ER positive/HER2 negative patients was associated with a significantly worse OS (HR = 2.04, 95% CI = 1.42 to 2.92) and significantly worse DFS (HR = 1.61, 95% CI = 1.23 to 2.11). On the other hand, there was no significant interaction found between the BMI and OS or DFS in ER negative/HER2 negative patients and HER2 positive patients. Subsequently, when analysis was limited to ER positive HER2 negative, there was a difference in the degree of association between obesity and prognosis due to the difference in menopause status. In premenopausal patients with ER positive/HER2 negative cancer, Obese group had significantly poorer OS (HR = 2.83, 95%CI = 1.32 to 5.88) and significantly poorer DFS (HR = 2.41, 95%CI = 1.41 to 3.99). In postmenopausal patients, Obese group patients had significantly poorer OS (HR = 1.71, 95%CI = 1.11 to 2.58) and poorer DFS (HR = 1.35, 95%CI = 0.98 to 1.86), however. The relevance was not so large compared with that in premenopausal patients. Conclusion : Among Japanese breast cancer patients, Obese (BMI ≥ 25 kg/m 2 ) was one of poor prognostic factors. Specifically, obesity was associated as an extremely strong prognostic factor in ER positive/HER2 negative premenopausal patients. Since hormone therapy has been practiced in almost all ER positive breast cancers, the relationship between hormonal therapy susceptibility and obesity is noticed not only in western patients but also in Asian patients. Citation Format: Sato M, Terai S, Tachikawa H, Maeda H, Yamamoto M, Tomioka N, Watanabe K, Takahashi M. Obesity is associated with poor prognosis of Japanese breast cancer, especially in ER positive/HER2 negative subtype, which tendency is prominent [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-07-13.