Differential impact of body mass index and its change on the risk of breast cancer by molecular subtype: A case-control study in Japanese women.
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/m(2) 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 P(trend) < 0.001). Additionally, we found the same tendency for the triple-negative subtype, with the OR for a 1 kg/m(2) increase in current BMI of 1.21 (1.05 - 1.39) and that for BMI change of 1.18 (1.02 - 1.36) (P(trend) 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, P(trend) = 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.


BACKGROUND
The online version of this article (doi:10.1186/2193-1801-1-39) contains supplementary material, which is available to authorized users.
Division of Epidemiology and Prevention, Aichi Cancer Center Research Institute, 1-1, Kanokoden, Chikusa-ku, Nagoya, 464-8681 Japan  ; Department of Breast and Endocrine Surgery, Kumamoto University Graduate School of Medical Science, 1-1-1, Honjo, Kumamoto, 860-8556 Japan.
Aiko
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Sueta
Hidemi
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Ito
Tania
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Islam
Satoyo
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Hosono
Miki
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Watanabe
Kaoru
K
Hirose
Takashi
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Fujita
Yasushi
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Yatabe
Hiroji
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Iwata
Kazuo
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Tajima
Hideo
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Tanaka
Hirotaka
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Iwase
Keitaro
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Matsuo