Impact of body mass index on breast cancer subtypes in Iranian women

Background: The incidence of obesity as one of the risk factors of breast cancer (BC) is increasing dramatically. Our objective was to evaluate the association between body mass index (BMI) and three subtypes of BC in Iranian women. Materials and Methods: In this retrospective study, BC patients' information was recorded by referring to their medical records in the Cancer Institute of Imam Khomeini Hospital, Iran, from 2015 to 2017. The data of 374 patients were entered into the study, and tumor data were classified into three groups by molecular markers (human epidermal growth factor receptor 2 [HER2] enriched, triple negative, and luminal). Results: Luminal subtype comprised the majority (71.1%) of all diagnosed BC patients. The proportion of obese women was higher in triple-negative group (35.3%), although the differences between three subtypes of BC were not statistically significant (P = 0.30). Multivariate logistic among cases only, considering luminal as the comparison group, indicated a positive association between age of menarche and HER2-enriched subtype (odds ratio [OR] = 1.18, 95% confidence interval [CI]: 0.99–1.41, P = 0.07) and also suggested a reverse association between age at time of diagnosis and triple-negative subtype (OR = 0.97, 95% CI: 0.95–1, P = 0.09) with borderline significance. Conclusion: We did not find any statistically significant differences in BMI between three subtypes of BC. It seems that there is a correlation between triple-negative subtypes of BC in Iranian population and obesity. However, further studies with larger sample size are needed.