Moreover, we also found a close correlation between MPO as well as CD66b and PADI4 (protein-arginine deiminase type-4, an essential enzyme to trigger citrullination of histone and initiate NETs) in two databases of TCGA and The Human Protein Atlas (Additional file 2: Figure S4), which further supported our finding of NETs forming in HCC. Here, PADI4 is linked to hepatocellular carcinoma.