Microsatellite instability and DNA mismatch repair in human cancer.

A form of genome instability in human tumours is associated with defects in a DNA mismatch repair pathway that normally corrects replication errors. The instability is observed as highly polymorphic mono- and dinucleotide microsatellites. Alterations in microsatellite length are due to accumulated frameshift mutations that arise because of uncorrected misalignments between template and daughter DNA strands during replication. Loss of mismatch repair is associated with some familial cancers, occurs at an early stage in tumour development and confers a general mutator phenotype. The latter may accelerate the accumulation of mutations in critical target genes during progression to malignancy. Biochemical analysis is providing insights into the mechanisms of mismatch repair.