The citrullination of histones by PAD4 has been detected in various types of cancers, such as acute myeloid leukemia (PAD4-H3), lung cancer (PAD4-CitH4R3), non-small cell lung cancer (PAD4-CitH4R3), gastric cancer (PAD4-CitH3R26), osteosarcoma (PAD4-CitH3) [10], and, like PAD2, prolactinoma (PAD4-CitH3R2, 8, 17) and breast cancer MCF-7 (PAD4-CitH3R17) [10,41]. The gene discussed is PADI4; the disease is osteosarcoma.