MMP12 and breast cancer: Genetically elevated serum MMP-12 level were not causally associated with risk of ER-negative BC (OR = 1.02, 95%CI: 0.96–1.07, P = 0.56), which was supported by the results of the other three datasets (ieu-a-1136: OR = 0.98, 95% CI: 0.91–1.05, P = 0.59; ieu-a-1137: OR = 0.95, 95%CI: 0.85–1.06, P = 0.35; ieu-a-1166: OR = 0.99, 95%CI: 0.92–1.07, P = 0.86) except GWAS ieu-a-1135 (OR = 1.07, 95%CI: 1.00–1.13, P = 0.04) (Table 5).