Colon tumor
Molecular pathways
Microsatellite instability pathway

Author: Shilpa Jain, M.D. New York University (see Authors page)

Revised: 22 December 2016, last major update September 2010

Copyright: (c) 2003-2016, PathologyOutlines.com, Inc.

PubMed Search: "Microsatellite instability pathway"
Cite this page: Microsatellite instability pathway. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/colontumormolecularmicrosatellite.html. Accessed May 28th, 2017.
Definition / general
  • Microsatellites, also called short tandem repeats, are repeating sequences of 1 - 6 base pairs of DNA (Wikipedia)
  • Microsatellite instability is characterized by widespread alteration in the size of repetitive DNA sequences caused by defective DNA mismatch repair
Terminology
  • Have high (MSI-H) or low levels of instability (MSI-L)
Epidemiology
  • Seen in 10 - 15% of sporadic carcinomas and hereditary nonpolyposis colon cancer (Gut Liver 2010;4:151)
Etiology
  • Due to either germline mutations (Lynch syndrome and variants) or sporadic due to promotion methylation
  • Due to alterations in mismatch repair genes MSH2, MSH6, MLH1, PMS2 and mitotic checkpoint regulator genes whose alterations cause gross chromosomal abnormalities (BUB1, BUBR1, CDC4, Cancer Metastasis Rev 2004;23:11)
  • Inactivation of both alleles of nucleotide mismatch repair, usually hMSH2 or hMLH1, promotes tumorigenesis
  • Tumors have numerous nucleotide substitutions and insertion / deletion mutations in microsatellites but normal total DNA content and relatively normal cytogenetics with only infrequent allelic gains / losses
  • Sporadic MSI-H cases arise predominantly through promoter hypermethylation and silencing of the hMLH1 gene
  • Herediatry MSI-H (hereditary nonpolyposis colorectal cancer) typically has germline mutations in one of the DNA mismatch repair genes (Nat Genet. 2006;38:787)
  • There may be different patterns of gene mutations in distal colon / rectum from proximal colon (BMC Cancer 2010;10:587)
Clinical features
  • Often present at earlier stage than other colon carcinomas
  • Tumors with MSI-H tend to be more proximally located, poorly differentiated, with mucinous histology and prominent lymphocytic infiltration and have been linked with TGFBRII and BRAF mutation (J Clin Pathol 2008;61:561)
  • Frequently present in colon / stomach double primaries (Mod Pathol 2001;14:543)
Prognostic factors
  • Although the prognosis is stage and grade dependent, tumors with identical morphological features display considerable heterogeneity in clinical outcome
  • Patients with MSI-H have a stage independent improved survival compared to patients with microsatellite stable (MSS) tumors in most, though not all studies but do not benefit from treatment with 5-fluorouracil in randomized adjuvant therapy trials (N Engl J Med 2003;349:247)
Microscopic (histologic) description