CXCL8 and synovial sarcoma: As for the inflammatory aspect, synovial biopsies from SS patients have demonstrated the expression of cytokines (e.g., IL-1β, IL-6, IL-8, matrix metalloproteinases, and tumor necrosis factor-alpha) and the chronic presence of immune cells (B and T lymphocytes, mast cells, and macrophages) in the stiff shoulders [24,25].