Abstract
Body mass index (BMI) is an independent risk factor for luminal-type breast cancer in Western populations. However, it is unclear whether the impact of BMI differs according to breast cancer subtype in Japanese populations. We conducted a case–control study with 715 cases and 1430 age- and menopausal status-matched controls to evaluate the associations of BMI and its change (from age 20 years to the current age) with breast cancer risk. We applied conditional logistic regression models to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Tumor subtypes were divided into four subtypes, namely the luminal, luminal/HER2, HER2-rich, and triple-negative subtypes. Current BMI and BMI change were positively associated with postmenopausal breast cancer risk. On stratified analysis by tumor subtype, we observed associations between current BMI and BMI change and postmenopausal breast cancer risk for the luminal subtype, with OR for each 1 kg/m2 increase in current BMI of 1.14 (95% CI: 1.07 - 1.20) and the corresponding OR of BMI change of 1.16 (1.09 - 1.23) (each Ptrend < 0.001). Additionally, we found the same tendency for the triple-negative subtype, with the OR for a 1 kg/m2 increase in current BMI of 1.21 (1.05 - 1.39) and that for BMI change of 1.18 (1.02 - 1.36) (Ptrend was 0.008 and 0.024, respectively). In premenopausal women, a suggestive inverse association was observed between BMI change and breast cancer risk for the luminal subtype only, with OR of BMI change of 0.93 (0.87 - 1.00, Ptrend = 0.054). No association was seen between BMI at age 20 years and risk of any tumor subtype. In conclusion, BMI and its change are associated with the risk of both luminal and triple-negative breast cancer among postmenopausal Japanese women. These findings suggest the etiological heterogeneity of breast cancer among tumor subtypes.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-1-39) contains supplementary material, which is available to authorized users.
Highlights
The rapid increase in the incidence rate of breast cancer over the last quarter of a century in Japan (Matsuda et al 2011) can be related to changes in the prevalence of established risk factors, such as reproductive and anthropometric factors (Minami et al 2004)
We previously showed that the general lifestyle of cancer-free outpatients at our hospital was in accord with that of a general population randomly selected from the electoral roll of Nagoya City, Aichi Prefecture, confirming the feasibility of their use as controls in epidemiological studies (Inoue et al 1997)
In this study, we evaluated the associations between current Body mass index (BMI), BMI at age 20 years, BMI change and breast cancer risk
Summary
The rapid increase in the incidence rate of breast cancer over the last quarter of a century in Japan (Matsuda et al 2011) can be related to changes in the prevalence of established risk factors, such as reproductive and anthropometric factors (Minami et al 2004). The clinical relevance of molecular subtypes of breast cancer has been demonstrated These appear to include at least four major tumor subtypes defined by ER, progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status, (Perou et al 2000; Sorlie et al 2001). Potential biological differences among cancers may be present, and the prevalence of obesity differs between Western and Asian countries These issues highlight the importance of evaluating the impact of BMI and its change on breast cancer risk by tumor subtype in Asian populations
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