Among these, seven cytokines including MCP-1/MCAF, IL-17, PDGF-BB, IL-18, FGF-BASIC, IL-1ra, and IL-2, exhibited positive mediating effect on immune cell traits to SCLC risk (range of OR, 1.18 [95% CI, 1.1784–1.387]) for IL-18 to 1.3957 [95% CI, 1.0172–1.915]) for FGF-BASIC, whereas IL-12p70, IL-6, and MCP-3 showed negative mediating effect on immune cell traits to SCLC risk (range of OR, 0.7896 [95% CI, 0.6319–0.9865] for IL-12p70 to 0.8772 [95% CI, 0.7809–0.9853] for MCP-3). This evidence concerns the gene CCL2 and small cell lung carcinoma.