A pooled case-only analysis of obesity and breast cancer subtype among Black women in the southeastern United States.

ABSTRACT

PURPOSE: To evaluate the association between obesity and the relative prevalence of tumor subtypes among Black women with breast cancer (BC). METHODS: We conducted a pooled case-only analysis of 1,793 Black women with invasive BC recruited through three existing studies in the southeastern US. Multivariable case-only polytomous logistic regression models were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the association between obesity, measured by pre-diagnostic body mass index (BMI), and human epidermal growth factor receptor 2 + (HER2 +) and triple negative BC (TNBC) subtype relative to hormone receptor (HR) + /HER2- status (referent). RESULTS: Among 359 premenopausal women, 55.4% of cases were HR + /HER2 -, 20.1% were HER2 + , and 24.5% were TNBC; corresponding percentages among 1,434 postmenopausal women were 59.3%, 17.0%, and 23.6%. Approximately, 50-60% of both pre- and postmenopausal women were obese (BMI > 30 kg/m2), regardless of BC subtype. We did not observe a significant association between obesity and BC subtype. Among postmenopausal women, class I obesity (BMI 35 + kg/m2) was not associated with the development of HER2 + BC (OR 0.69; 95% CI 0.42-1.14) or TNBC (OR 0.93; 95% CI 0.60-1.45) relative to HR + /HER2- tumors. Corresponding estimates among premenopausal women were 1.03 (95% CI 0.43-2.48) and 1.13 (95% CI 0.48-2.64). CONCLUSION: In this large study of Black women with BC, there was no evidence of heterogeneity of BMI by BC subtype.