Abstract 3654: Associations of body mass index and its change with breast cancer risk by molecular subtypes: a case-control study in Japanese women.
Authors: Sueta Aiko , Ito Hidemi , Islam Tania , Hosono Satoyo , Watanabe Miki , Iwata Hiroji , Tajima Kazuo , Tanaka Hideo , Matsuo Keitaro , Iwase Hirotaka 
Published: August 2014

Abstract
Introduction. Recently, the clinical relevance of molecular subtypes of breast cancer has been demonstrated, but the evidence on etiologic differences among them is limited. Some epidemiological studies in Western populations have shown that body-mass-index (BMI) is a risk factor for luminal-type breast cancer. However, it is unclear whether the impact of BMI on the risk differs among tumor subtypes in Japanese population. Methods. We conducted a case-control study with 715 case subjects and 1430 age- and menopausal status-matched controls to evaluate the associations of BMI at current age, age at 20 years, and its change (from age 20 years to the current age) with the breast cancer risk. We applied conditional logistic regression models to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Tumor subtypes were determined by estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor 2(HER2) and divided into four subtypes: luminal, luminal / HER2, HER2-rich, and triple-negative subtype. Results. Current BMI and BMI change were positively associated with the risk of postmenopausal breast cancer. On stratified analyses by tumor subtype, we observed the associations between current BMI, BMI change and thepostmenopausal breast cancer risk for luminal subtype; OR for each 1 kg/m2increase of current BMI was 1.14 (95%CI: 1.07 - 1.20) and the corresponding OR of BMI change was 1.16 (1.09 - 1.23) (each Ptrend &lt; 0.001). Additionally, we found the same tendency for triple-negative subtype; the OR for 1 kg/m2 increase of current BMI was 1.21 (1.05 - 1.39), and that for BMI change was 1.18 (1.02 - 1.36) (Ptrend was 0.008 and 0.024, respectively). No significant associations among them were seen for the other subtypes. In premenopausal women, the suggestive inverse association was observed between BMI change and breast cancer risk only for luminal subtype; OR of BMI change was 0.93 (0.87 - 1.00, Ptrend= 0.054). There were no associations between BMI at age 20 years and the risk for any tumor subtypes. Conclusions. BMI and its change are associated with the risk of both luminal and triple-negative breast cancer among postmenopausal women, despite the molecular and clinical differences between these two subtypes. Our results provide additional evidence for an etiological heterogeneity of breast cancer among tumor subtypes.
Citation Format: Aiko Sueta, Hidemi Ito, Tania Islam, Satoyo Hosono, Miki Watanabe, Hiroji Iwata, Kazuo Tajima, Hideo Tanaka, Keitaro Matsuo, Hirotaka Iwase. Associations of body mass index and its change with breast cancer risk by molecular subtypes: a case-control study in Japanese women. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3654. doi:10.1158/1538-7445.AM2013-3654