A desmoplastic response is characterized by larger stromal cells with increased extracellular fibers and immunohistochemically by transformation of fibroblastic-type cells to a myofibroblastic phenotype.[2] Myofibroblastic cells in tumors are differentiated from fibroblasts for their positive staining of smooth-muscle actin (SMA).[2] Furthermore, an increase in total fibrillar collagens, fibronectins, proteoglycans, and tenascin C are distinctive of the desmoplastic stromal response in several forms of cancer.[14] Expression of tenascin C by breast cancer cells has been demonstrated to allow for metastasis to the lungs and cause the expression of tenascin C by the surrounding tumor stromal cells.[15] In addition, tenascin C is found extensively in pancreatic tumor desmoplasia as well.[16]