Notably, 14 autoimmune diseases—including SLE, RA, antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, Sjogren’s syndrome (SS), systemic sclerosis (SSc), type 1 diabetes (T1D), Behçet disease (BD), multiple sclerosis (MS), psoriasis, autoimmune thyroid diseases (AITDs), myasthenia gravis (MG), giant cell arteritis (GCA), Takayasu’s arteritis (TAK), and inflammatory bowel disease (IBD)—have demonstrated associations with IL-9. This evidence concerns the gene IL9 and synovial sarcoma.