The inverse association with IL-15 was strongest >7.1 years prior to brain cancer diagnosis (HR = 0.75; 95% CI: 0.61, 0.92) and within 1.8–1.0 years of diagnosis (HR = 0.77, 95% CI: 0.63, 0.95), as well as in individuals ≥35 years old at cancer diagnosis (HR = 0.72; 95% CI: 0.58, 0.90). Here, IL15 is linked to brain cancer.