For patients with non-cancer-related pain, after adjusting for sociodemographic, disease-specific, MME, and psychiatric variables as well as patients’ daily morphine equivalent, the PEG was not significantly associated with circulating cytokine levels for IL-1β (β = 0.022, 95% CI = −0.031–0.074, p = 0.413), IL-1α (β = 0.022, 95% CI = −0.034–0.078, p = 0.435), TNF-α (β = −0.009, 95% CI = −0.025–0.006, p = 0.234), IFN-γ (β = 0.019, 95% CI = −0.032–0.070, p = 0.463), IL-2 (β = −0.008, 95% CI = −0.030–0.046, p = 0.675), or IL-10 (β = 0.020, 95% CI = −0.022–0.061, p = 0.348). The gene discussed is IL1B; the disease is cancer.