IL13 and breast cancer: We systematically screened 41 cytokines (of which 24 cytokines have available instruments) and identified that genetically predicted circulating levels (1-SD increase) of MCP1 (OR: 1.08; 95% CIs: 1.03–1.12; P value: 3.55 × 10−4), MIP1b (OR: 1.02; 95% CIs: 1.01–1.04; P value: 2.70 × 10−3) and IL13 (OR: 1.06; 95% CIs: 1.03–1.10; P value: 3.33 × 10−4) were significantly associated with increased risk of overall BC, as well as ER-positive BC.