Here we present results from a pooled analysis of data from three population-based breast cancer case-control studies conducted among white women and African-American women [6–8]; we examine the associations between BMI at age 18 years and BMI 5 years before case patients’ breast cancer diagnosis or control participants’ index date (herein referred to as “recent BMI”) in relation to risk of breast cancer overall and risk of breast cancer subtypes defined by ER, PR, and HER2. The gene discussed is ESR1; the disease is breast cancer.