title: Does MSI-low exist?
abstract: Microsatellite instability is a well-recognised phenomenon. Ten to 15% of sporadic colorectal cancers with a high level of MSI form a well defined group with distinct clinicopathological features. The set of tumours with low level of microsatellite instability (MSI-low), though widely referred to, is not a clearly defined group. The definitions of MSI-low have varied among groups and between different studies from the same group. Some studies have found associations between the MSI-L phenotype and molecular features, notably a higher frequency of K-ras mutations, and, possibly, methylation of methylguanine methyltransferase. Two recent independent studies, however, showed respectively that 68% and 79%, non-MSI-H cancers showed some MSI and could therefore be classed nominally as MSI-L. There was no evidence for a qualitatively discrete MSI-L group, but quantitative differences in the level of MSI were found.
authors.affiliation: Molecular and Population Genetics Laboratory, Imperial Cancer Research Fund, London, UK. i.tomlinson@icrf.icnet.uk
authors.forename: Ian
authors.initials: I
authors.lastname: Tomlinson
authors.forename: Sarah
authors.initials: S
authors.lastname: Halford
authors.forename: Lauri
authors.initials: L
authors.lastname: Aaltonen
authors.forename: Nicholas
authors.initials: N
authors.lastname: Hawkins
authors.forename: Robyn
authors.initials: R
authors.lastname: Ward
mesh_terms: D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D006801:Humans; D018895:Microsatellite Repeats