DNMT1 and neoplasm: On the other hand, our previous meticulous microdissection technique and immunohistochemistry have revealed that peripheral pancreatic duct epithelial cells, i.e., the origin of ductal adenocarcinoma (Hruban et al. 1997), and not surrounding lymphocytes or fibroblasts, actually show cumulative DNA methylation abnormalities of tumor-related genes associated with aberrant expression of DNMT1 at the precancerous N stages (Peng et al. 2005, 2006).