Body mass index and risk of breast cancer molecular subtypes in Korean women: a case control study

Abstract

Background: Obesity has been suggested as a risk factor for postmenopausal breast cancer. However, the effects of obesity on developing different subtypes of breast cancer remain unclear, particularly for premenopausal women. Methods: This study aims to evaluate the association between body mass index (BMI, kg/m2) and risks of the subtypes including Luminal A (ER and PgR + and HER2- and Ki-67<14%), Luminal B-HER2 negative (ER + and HER2 - and (Ki-67≥14% or PgR -)), Luminal B-HER2 positive (ER + and HER2 + and any Ki-67, any PgR), HER2-express (ER- and PgR- and HER2 + ), Triple negative (ER- and PgR- and HER2 - ). Based on a community-based case-control study design, a total of 101,274 female breast cancer patients (35-80 years old) diagnosed between 2003 and 2010 were individually matched by age to healthy women (1:2 ratios of cases and controls). Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using multivariate logistic regression with normal weight (BMI 18.5-22.9) as the reference group of exposures. Results: For post-menopausal women, breast cancer risk of Luminal B-her negative type increased in the obese II group (BMI≥30) (OR: 3.22 CI: 2.41-4.31), which showed similar results for other subtypes. For pre-menopausal women, being underweight (BMI <18.5) was related to increased risk of Luminal A (OR: 1.23 CI: 1.09-1.39). In addition, the obese II group (BMI≥30) was more likely to develop basal-like breast cancer (OR: 1.63 CI: 1.29-2.05). For those with BC family history for pre-menopausal women, being underweight (BMI <18.5) was related to increased risk of HER2 express (OR: 2.41 CI: 1.21-4.80) and Triple-negative (OR: 1.98 CI: 1.22-3.22). Conclusions: Our findings suggest that BMI can be an important predictor of the breast cancer subtypes for both post- and pre-menopausal women.