Body Mass Index as a Risk and Prognostic Factor of Breast Cancer

ABSTRACT

PURPOSE: In order to study the effect of body mass index (BMI) on the risk and the prognosis of breast cancers, we analyzed the BMI and clinico-pathological data of the breast cancer patients. We compared the BMIs of breast cancer patients to those of normal women and investigated the association of the BMI with the clinico-pathological data. Then the overall and disease-free survial probabilities were analyzed according to the BMI groups. METHODS: 1,201 breast cancer patients were available for the analysis of BMI and the BMI of the normal control women was adopted from the report of the National Health, Nutrition Survey of 1998. We classified the BMI groups by he World Health Organization classification as follows; BMI under 18.5 as under-weight group, 18.5-24.9 as the normal weight group, 25-30 as the overweight group, and over 30 as the obesity group. BMI was compared between the patient group and the control group by age, while the correlation between BMI and the clinico-pathological characteristics and the recurrence and survival rates for each BMI group were comparatively analyzed. The statistical analysis were performed using x2 test, one-way ANOVA, independent T-test, and one sample T test, and the survival probabilities were generated by Kaplan-Meier methods. RESULTS: The means of BMI increased by aging in both the patients and the control group. The means of BMI of the 30s and 50s were significantly lower in breast cancer patients than those of normal women (P=0.001, 0.002). However, those of 60s and 70s were higher in breast cancer patients with marginal significance (P=0.159). In the pre- menopausal patient group, BMI was associated with the tumor size (P=0.012) and the tumor stage (P=0.018). In the post-menopausal patients, on the other hand, BMI had positive relationship with well-differentiation of the tumor (P=0.025), and also showed a marginal association with estrogen receptor positivity (P=0.074). BMI did not influence on the outcome of premenopausal breast cancer patients but lower BMI (underweight group) showed poorer outcome in postmenopausal patients in terms of overall survival (P= 0.278), locoregional relapse-free survival (P=0.581), and distant relapse-free survival (P=0.040). CONCLUSIONS: As a breast cancer risk factor, BMI seems to have a different association by the age. Higher BMI for the 60s and 70s but lower BMI for the younger age group seems to be a risk factor for the breast cancer development. In terms of the relationship with the clinico-pathological characteristics, BMI has different association by the menopausal status. BMI did not influence on the outcome of premenopausal breast cancer patients but lower BMI (underweight group) showed significantly poorer outcome in postmenopausal patients.