Al-dujaili, Amar H., et al. “Comparative Study of CA19-9 Levels As Tumor Marker in Sera and Tissues of Patients With Stomach, Colon and Rectum Cancers”. Journal of the Faculty of Medicine Baghdad, vol. 51, no. 2, July 2009, pp. 223-6, https://doi.org/10.32007/jfacmedbagdad.5121218.