During the bidirectional MR, results showed no evidence of BC causally influencing the levels of MCP1 (OR: 1.00; 95% CIs: 0.95–1.04; P value: 0.885), MIP1b (OR: 1.01; 95% CIs: 0.97–1.06; P value: 0.573) and IL13 (OR: 1.03; 95% CIs: 0.96–1.11; P value: 0.380). This evidence concerns the gene CCL4 and breast cancer.