sentences:  MiR-155 targets MLH1 and MSH2 and an inverse correlation between the expression of miR-155 and the expression of MLH1 or MSH2 proteins was found in human colorectal cancer.A field defect is an area or "field" of epithelium that has been preconditioned by epigenetic changes and/or mutations so as to predispose it towards development of cancer.As pointed out by Rubin, "The vast majority of studies in cancer research has been done on well-defined tumors "in vivo," or on discrete neoplastic foci "in vitro."