Microsatellite instability pathway

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"

Table of Contents

Cite this page: Microsatellite instability pathway. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/colontumormolecularmicrosatellite.html. Accessed July 26th, 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

Includes medullary, mucinous and signet ring carcinoma subtypes (Am J Surg Pathol 2003;27:1393)