Results showed no significant causal associations between GBM and levels of CCL25 (OR = 1.01, 95% CI = 0.99–1.03, P = .519), M-CSF1 (OR = 1.01, 95% CI = 1.00–1.03, P = .125), FGF21 (OR = 1.01, 95% CI = 0.99–1.03, P = .406), and IL-33 (OR = 0.99, 95% CI = 0.97–1.01, P = .463). This evidence concerns the gene IL33 and glioblastoma.