Genetically elevated serum MMP-1 level were causally associated with a low risk of ER-negative BC (OR = 0.92, 95% confidence interval [CI]: 0.88–0.97, P = 0.0008), which was validated in the other three datasets as suggestive associations (ieu-a-1135: OR = 0.93, 95% CI: 0.87–0.99, P = 0.03; ieu-a-1136: OR = 0.92, 95% CI: 0.86–1.00, P = 0.049; ieu-a-1166: OR = 0.92, 95% CI: 0.85–1.00, P = 0.047) (Table 1). This evidence concerns the gene MMP1 and breast cancer.