IL9 and diffuse large B-cell lymphoma: If the serum IL-9 level ≥1 pg/ml was defined as positive expression, IL-9 was detected in 24 of 30 sera from DLBCL patients (mean concentration 1.43 ± 0.64 pg/ml) while no serum samples from healthy volunteers contained marginally detectable levels of IL-9 (0.82 ± 0.15 pg/ml).