Assessment of Carcinoembryonic Antigen-Related Cell Adhesion Molecules (CEACAM6) in Pancreatic Ductal Adenocarcinoma, A Combined Serum and Immunohistochemical Study, MOSTAFA M. AMER, GHADA A. ABD EL-FATTAH, MOHEBAT H. GOUDA, RASHA M. EL-SAWI, EBADA M. SAEED and AHMED ZEEDAN