P4-09-25: Impact of Body Mass Index (BMI) for Clinical Outcomes in Japanese Breast Cancer Patients

Background: Obesity is risk factor of breast cancer incidence in postmenopausal women including Japanese population. Currently, many clinical trials data were shown that obesity may be one of prognostic factors after primary treatment in postmenopausal breast cancer patients. However, the proportion of obesity is large different between Asain and Western populations in all breast cancer patients. There is a little paper about relationship between body mass index (BMI) and prognosis after surgery in Asian breast cancer population.

Methods: We conducted retrospective analysis about BMI and outcome after primary treatment in Japanese breast cancer patients. We reviewed the clinical data (height, weight, BMI, ER status, HER status, and outcome) based on our medical reports in our single institution. This research object is 1,100 patients with primary breast cancer who operated between Jan 2003 and Jan 2006 in our institution. Median follow up was 59 months (1-97). All patients are categorized into four groups according to BMI. The range of BMI is less than 18.5 kg/m2, from 18.5 to 24.9 kg/m2, 25 to 29.9 kg/m2, more than 30 kg/m2 in underweight, normal, overweight and obesity groups, respectively. Patient's characteristics are well balanced excluding age and menopausal status. Nobody is obesity in young women (less than 35 years old). The correlation BMI with disease free survival (DFS) and overall survival (OS) were statistically analyzed by using the Cox hazard model.

Results: 785 (71.3%), 88 (8%), 192 (17.5%), 35 (3.2%) patients were categorized into normal, underweight, overweight obesisty groups, respectively. Breast cancer recurrences including local and distant metastases were occurred in 126 patients (11.5%).66 (6%) patients died due to breast cancer recurrence (54 patients) and other disease (8 patients). The multivariate hazard ratio (HR) in obesity groups was tend to be high compared with normal groups in disease free survival and overall survival. HR for OS was 4.30 (95%CI, 1.79−10.3) in obesity group. However, there are no statistical significant differences among four groups. Especially, HR for DFS and OS was 2.90 (95% CI 1.15−7.30 p=0.024) and 7.05(95%CI 2.38−20.8 P<0.001) in obesity group compared with normal group in ER positive patients, respectively. However, there are no statistical significant difference for DFS and OS among four groups in ER negative patients.

Conclusions: The proportion of obesity is very lower in Japanese population (3.2%) than Western population (about 25–30%). However, obesity might be risk factor for DFS and OS in Japanese breast cancer patients with ER positive similar with Western countries. The different proportion of BMI may be influenced the different overall survival rate in lymph node negative breast cancer patients between Japan and Western countries. This study is a first report of the association between obesity and clinical outcomes in Japanese breast cancer patients. However, a number of patients were limited and this study is retrospective analyses including heterogeneous subtypes in single institution. A large scale cohort study should be conducted based on the clinical trial in Japanese population.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-09-25.