Microsatellite Instability (MSI)


MSI is a change in length of a microsatellite allele due to insertion or deletion of repeating units during DNA replication and failure of the DNA mismatch repair system to correct these errors.  Samples with instability in two or more markers are defined as MSI-High (MSI-H) whereas those with one unstable marker are designated as MSI-Low (MSI-L).  Samples with no detectable alterations are MSI-stable (MSS).

Referral information

We accept biopsies or resection samples from patients with a possible diagnosis of Lynch syndrome.   MSI testing is also available in the context of contributing to decision-making regarding chemotherapy administration. Formalin-fixed paraffin-embedded (FFPE) material should have been reviewed by a pathologist to determine suitability for testing and an estimate of tumour cell content is required. We require either 5 x 5µm unstained, slide-mounted sections or unmounted sections from tissue blocks containing a) tumour tissue and b) normal tissue.  A 20% ratio of neoplastic to normal cells in the submitted pathology sample is required for reliable MSI assessment. Samples with lower tumour cell content may be acceptable but wherever possible should be accompanied by a representative H&E stained slide with areas of tumour marked to allow for macrodissection. Please contact the laboratory for guidance if you are unsure whether a sample is suitable.

Price & reporting times

NHS referrals to this service are paid for where there is an existing specialist commissioning contract for genetic testing.

Test Price (NHS) Price (non-NHS) TRT (calendar days)
MSI POA POA 28 calendar days

Test validation & quality assurance - information for users

5 x 5µM FFPE unstained slide mounted sections (without coverslips) from tissue blocks containing both a) tumour tissue and b) normal tissue. If neoplastic cell content of the tumour sample is less than 20% and the sample is suitable for macrodissection, please send an accompanying H&E stained guide slide prepared from a neighbouring section with the region of neoplasia.  Where neoplastic cell content is greater than 30%, 5 x 5 µM FFPE sections from both a) tumour tissue and b) normal tissue blocks as unmounted scrolls in a clean, unused, tube or container manufactured under aseptic conditions is acceptable.

Referral guidelines

Please see our referral guidelines for more information.