[Product Promotion] MSI Standard Products

Microsatellite Instability (MSI) refers to the phenomenon that the length of the microsatellite (MS) sequence changes due to insertion or deletion mutations during DNA replication. It is often caused by the mismatch repair function (Mismatch repair, MMR). Caused by defects. MS sequences are short and repetitive DNA sequences, generally composed of 1 to 6 nucleotides, arranged in tandem and repeated, and the common types are double base CA/GA/GT or single base A/T. The MS sequence can be located in the important non-coding region of the gene, or in the coding region of the gene. The polymorphisms are distributed throughout the genome and individual differences are large. The MSI phenomenon was first discovered in colorectal cancer by Jacobs et al. in 1993. It is related to the occurrence of cancer and can be used for cancer detection.

MSI is often caused by MMR gene mutation and loss of function. Therefore, when detecting MSI in cancer cells, MSI can be determined by detecting MMR gene deletion, such as protein level detection that relies on immunohistochemistry technology, or directly detecting MSI sequence changes, such as PCR (polymerase Chain reaction) detection and other molecular level detection.

Immunohistochemistry (Immunohistochemistry, IHC): Immunohistochemistry was used to detect the expression of mismatch repair genes MLH1, MSH2, MSH6 and PMS2 in tumor tissues. Any mismatch repair gene expression loss is defined as MSI, otherwise it is microsatellite stabilization (MSS). One expression loss is called low-grade microsatellite instability (MSI-L), and two or more protein expression loss is called high-grade microsatellite instability (MSI-H).

Molecular detection：

1. Polymerase chain reaction (PCR) technology

Currently, multiple fluorescent PCR combined with capillary electrophoresis is mainly used. The specific microsatellite repeat sequence amplification was detected by PCR to determine the MSI status, and the site mutations of the specimen tissues of tumor patients and normal tissues were compared. The comparison sites are five microsatellite sites recommended by the National Cancer Institute (NCI): BAT25, BAT26, D5S346, D2S123 and D17S250. Among them, the change of ≥2 sites is judged as high degree of microsatellite instability (MSI-H), only one site change is judged as low degree of microsatellite instability (MSI-L), and no site change is judged as microsatellite Stable (MSS). Some studies believe that the specificity and sensitivity of dinucleotide repetitive sequences are lower than that of single nucleotide repetitive sequences, so there is still controversy about the most suitable site for MSI detection. Bacher et al. evaluated the sensitivity and accuracy of detection of 266 microsatellite loci (including single nucleotide, dinucleotide, tetranucleotide and pentanucleotide microsatellite loci) and proposed the Promega analysis System, the system uses five single nucleotide microsatellite sites (BAT-25, BAT-26, NR-21, NR-24 and MONO-27) and two pentanucleotide microsatellite sites (Penta C And Penta D) detect MSI. A large number of experiments have confirmed that the results of MMR immunohistochemical detection are highly correlated with the results of PCR detection of MS, with a sensitivity of 92% and a specificity of up to 100%.

2. Next Generation Sequencing (NGS)

NGS, also known as second-generation sequencing technology, is a high-throughput sequencing technology that can sequence hundreds of thousands to millions of gene molecules at a time. At present, the NGS method has become a new tool for detecting MSI, and its biggest advantage is that it can achieve multi-site high-throughput detection. A study at the Memorial Sloan Kettering Cancer Center (MSK) used NGS methods to detect 12,288 solid tumor patients to determine the MSI status, and verified it with MSI-PCR/MMR-IHC. Experiments have proved that the NGS method is more sensitive than the MSI-PCR method.

We can provide MSI diagnostic standards to ensure the detection limit, sensitivity and stability of the diagnostic method.