Higher BI‐RADS breast density was strongly associated with increased risk of all four subtypes, with the largest HRs for ER/PR−HER2+ breast cancer (HR for BI‐RADS D = 6.90, 95% CI 1.35–87.7), though the confidence intervals are wide given the small number of cases in this subtype. The gene discussed is ESR1; the disease is breast carcinoma.