Alpha 1-Antichymotrypsin is an acute phase glycoprotein that functions by inhibiting proteases secreted by neutrophils and mast cells during periods of inflammation.  It is primarily produced by hepatocytes and locally expressed in histiocytes, including macrophages and Kupffer cells in the liver.  Alpha 1-Antichymotrypsin is a useful marker for malignant fibrous histiocytomas to aid in differentiating from other soft-tissue tumors such as liposarcomas or Ewing’s sarcoma.