Both overweight and obesity were associated with risk of estrogen receptor positive (ER+) disease (HRadj 1.20, 95% CI 1.00–1.44 and HRadj 1.33, 95% CI 1.03–1.71, respectively), and low-grade tumors (HRadj 1.25, 95% CI 1.02–1.54, and HRadj 1.40, 95% CI 1.05–1.86, respectively). This evidence concerns the gene ESR1 and Obesity.