Following exclusion of SNP rs7621046 in the restrictive MR analysis, genetically raised MIP1b was still associated with higher risk of any BC (OR: 1.02; 95% CIs: 1.01–1.03; P value: 1.80 × 10−3), while Cochran Q test for the heterogeneity didn’t reject the null hypothesis (Cochran P value: 0.151). This evidence concerns the gene CCL4 and breast cancer.