Biomarker: Microsatellite instability

Biomarker subtype: gene

Clinical application: prognosis(unfavorable)

Histology type: endometrioid endometrial carcinoma

Stage: stage I

Country: Norway

Region: Stavanger

Followed up time : 66 months (1-209),

Protocol age: 66;37–94

Sample type : tissue

Clinical method: immunohistochemical /tissue microarrays,image cytometry/PCR

Expression pattern : low p21(<1%) , high survivin expression(>158) and high microsatellite instability

Expression elevation: Microsatellite instability in any marker was visualized as changes in the product length. Instability in ≥40% (≥2 of 5) of the markers was regarded as high-frequency microsatellite instability, in 1 of 5 as low frequency and in no markers as microsatellite stable.

Statictics: Median;Range

Protocol age: 66;37–94

Description: We conclude that low p21 and high survivin expression are poor prognosis indicators in FIGO stage I endometrial endometrioid adenocarcinoma, especially when high microsatellite instability occurs.

Survival figure legend: Survival curve of the FIGO I endometrioid endometrial cancer patients

Survival curve link: https://www.nature.com/articles/modpathol201175/figures/1

Expression figure legend: Favorable combination of biomarkers p21.$ Unfavorable combination of biomarkers p21, survivin and microsatellite instability.

Expression figure link: https://www.nature.com/articles/modpathol201175/figures/2 $https://www.nature.com/articles/modpathol201175/figures/3

Detailed Description: Microsatellite instability (MSI) is the condition of genetic hypermutability (predisposition to mutation) that results from impaired DNA mismatch repair (MMR). The presence of MSI represents phenotypic evidence that MMR is not functioning normally. MMR corrects errors that spontaneously occur during DNA replication, such as single base mismatches or short insertions and deletions. The proteins involved in MMR correct polymerase errors by forming a complex that binds to the mismatched section of DNA, excises the error, and inserts the correct sequence in its place.[ Ehrlich M, ed. (2000). DNA alterations in cancer: genetic and epigenetic changes. Natick, MA: Eaton Publ. p. 178. ISBN 978-1-881299-19-6.] Cells with abnormally functioning MMR are unable to correct errors that occur during DNA replication and consequently accumulate errors. This causes the creation of novel microsatellite fragments. Polymerase chain reaction-based assays can reveal these novel microsatellites and provide evidence for the presence of MSI. Microsatellites are repeated sequences of DNA. These sequences can be made of units of 1 to 6 base pairs in length that are repeated and reside adjacent to each other in the genome. Although the length of microsatellites can vary from person to person and contributes to the individual DNA "fingerprint", each individual has microsatellites of a set length. The most common microsatellite in humans is a dinucleotide repeat of the nucleotides C and A, which occurs tens of thousands of times across the genome. Microsatellites are also known as simple sequence repeats (SSRs).[wikipedia] Structure Microsatellite instability structure consists of repeated nucleotides, most often seen as GT/CA repeats.[ Schl?tterer C, Harr B (March 2004). Microsatellite Instability (PDF). eLS. doi:10.1038/npg.els.0000840. ISBN 978-0470016176.] Researchers have yet to confirm the precise definition of the MSI structure. While all researchers agree that microsatellites are repeat sequences, the lengths of the sequences remain in question. Some research suggests that MSIs are short tandem DNA repeat sequences of one to six base pairs throughout the genome, while other research suggests that the range may be two to five.[doi:10.1016/j.dld.2012.10.006.] Although researchers do not agree on a specific threshold for the number of tandem repeats that constitute a microsatellite, there is a consensus around their relative size. Longer sequences are called minisatellite, and even longer sequences are called satellite DNA sites. Some scientists distinguish among the three categories by a minimum number of base pairs, and others use a minimum number of repeated units. The majority of repeats occur in untranslated regions, specifically introns. However, microsatellites that occur in coding regions often inhibit the expansion of most downstream events. Microsatellites make up approximately three percent of the human genome, or more than one million fragments of DNA. Microsatellite density increases with genome size and is seen twice as much at the ends of chromosome arms than in the chromosome bodies.[ PMID 15153996] Mechanism In a broad sense, MSI results from the inability of the mismatch repair (MMR) proteins to fix a DNA replication error. DNA replication occurs in the "S" phase of the cell cycle; the faulty event creating an MSI region occurs during the second replication event. The original strand is unharmed, but the daughter strand experiences a frame-shift mutation due to DNA polymerase slippage. Specifically, DNA polymerase slips, creating a temporary insertion-deletion loop, which is usually recognized by MMR proteins. However, when the MMR proteins do not function normally, as in the case of MSI, this loop results in frame-shift mutations, either through insertions or deletions, yielding non-functioning proteins.[PMID 20420947] MSI is unique to DNA polymorphisms in that the replication errors vary in length instead of sequence. The rate and direction of the mutations yielding MSIs are the major components in determining genetic differences. To date, scientists agree that the mutation rates differ in loci position. The greater the length of the MSI, the greater the mutation rate.[PMID 15153996] Although most mutations of MSI are the result of frame-shift mutations, occasionally the mutation events leading to MSI are derived from the hypermethylation of the hMLH1 (MMR protein) promoter. Hypermethylation occurs when a methyl group is added to a DNA nucleotide, resulting in gene silencing, thus yielding MSI.[PMID 14963101] Researchers have shown that oxidative damage yields frame-shift mutations, thus yielding MSI, but they have yet to agree on a precise mechanism. It has been shown that the more oxidative stress is placed on the system, the more likely it is that mutations will occur. Additionally, catalase reduces mutations, whereas copper and nickel increase mutations by increasing reduction of peroxides. Some researchers believe that the oxidative stress on specific loci results in DNA polymerase pausing at those sites, creating an environment for DNA slippage to occur.[PMID 9770509] Researchers first believed that MSI was random, but there is evidence suggesting that MSI targets include a growing list of genes. Examples include the transforming growth factor Beta receptor gene and the BAX gene. Each target leads to different phenotypes and pathologies.[PMID 17942460] Clinical significance Microsatellite instability is associated with colon cancer, gastric cancer, endometrium cancer, ovarian cancer, hepatobiliary tract cancer, urinary tract cancer, brain cancer, and skin cancers. MSI is most prevalent in associations with colon cancers. Each year, there are over 500,000 colon cancer cases worldwide. Based on findings from over 7,000 patients stratified for MSI-High (MSI-H), MSI-Low (MSI-L), or Microsatellite Stable (MSS) colon cancers, those with MSI-H tumours had a more positive prognosis by 15% compared to MSI-L or MSS tumors.[PMID 15659508].[wikipedia]