Loss of either MTAP protein or the MTAP gene is frequent in a large number of different human tumors, including leukemias, lymphomas, mesothelioma, lung carcinoma, pancreatic carcinoma, squamous cell carcinoma, biliary tract cancer, glioblastoma, osteosarcoma, and neuroendocrine tumors (Stadler and Olopade 1996; Dreyling et al. 1998; Hori et al. 1998; Schmid et al. 1998; Wong et al. 1998; Brat et al. 1999; M’soka et al. 2000; Garcia-Castellano et al. 2002; Illei et al. 2003; Chen et al. 2004; Subhi et al. 2004; Hustinx et al. 2005; Karikari et al. 2005). This evidence concerns the gene MTAP and biliary tract cancer.