PTGER4 and breast carcinoma: We addressed whether: (a) the native tube forming capacity of the LEC on Matrigel is dependent on COX-2 or EP4 activity; (b) soluble products of COX-2-expressing breast cancer cells stimulate tube formation by the LEC; (c) proliferation, migration and tube forming capacity of the LEC are stimulated by exogenous PGE2 or selective EP4 agonists and if so, what are the underlying signaling mechanisms.