FN1 and angiosarcoma: We compared the expression of angiosarcoma ECM proteins and their regulators to those found in non- diseased endothelium, observing positive antigenicity for fibronectin, collagen I, collagen IV, collagen V, collagen VI, MMP1, MMP2, and MMP13 in 6 angiosarcoma tumors and 10 non-diseased vascular tissues (Figure 1A).