ESR1 and neoplasm: According to tumor characteristics, we observed an association of the Lys/Lys genotype with ER‐positive BC (OR = 1.19, 95% CI 1.05–1.36, p = 0.008), PR‐positive BC (OR = 1.19, 95% CI 1.03–1.36, p = 0.015), and HER2‐negative BC (OR = 1.25, 95% CI 1.05–1.48, p = 0.012), but not with ER‐negative BC (OR = 1.07, 95% CI 0.90–1.27, p = 0.453), PR‐negative BC (OR = 1.13, 95% CI 0.95–1.34, p = 0.176), or HER2‐positive BC (OR = 1.19, 95% CI 0.97–1.48, p = 0.102), although no statistically significant heterogeneity was observed by tumor characteristics.