Clinical Practice Guidelines - National Health and Medical Research ...

14.5.1 Microsatellite instability
It is now apparent that DNA microsatellite instability falls into a high category (MSI-H), in which at
least 30% or more of the loci tested show instability and a low category (MSI-L). 19,20 Only the MSI-H
category shows distinctive clinical, pathological and molecular characteristics. These include:
• proximal location
• lower stage
• lower frequency of distant spread
• improved survival
• increased frequency of cancer multiplicity
• diploidy
• poor or mucinous differentiation and tumour infiltrating lymphocytes.
Between 9% and 16% of Colorectal Cancers are MSI-H. By contrast, MSI-L cancers are
indistinguishable from microsatellite stable cancers. 19,20
It is likely that further studies on tumour markers will provide more information on the expected
behaviour of Colorectal Cancers.
Staging and reporting 165