CCL4 and breast cancer: Among the potentially modifiable cytokine factors, MIP1b which has the most instrumental SNPs, contributes to higher BC risk (OR: 1.02; 95% CIs: 1.01–1.04; P value: 2.70 × 10−3), especially in ER-negative BC cases (OR: 1.04; 95% CIs: 1.02–1.06; P value: 7.69 × 10−4).