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Views: 0 Author: Site Editor Publish Time: 2026-06-17 Origin: Site
Microsatellite instability, commonly known as MSI, is a molecular change caused by defects in the DNA mismatch repair system. It occurs when short, repetitive DNA sequences called microsatellites become longer or shorter than normal due to insertion or deletion errors during DNA replication.
MSI is an important biomarker in cancer diagnostics. It is widely used in the evaluation of several solid tumors, especially colorectal cancer and endometrial cancer. MSI testing can help support Lynch syndrome screening, cancer prognosis evaluation, and treatment decision-making.
For laboratories, in vitro diagnostic developers, and oncology researchers, understanding MSI is essential for building reliable molecular testing workflows.
Microsatellites are short, repetitive DNA sequences distributed throughout the human genome. They usually consist of repeated units of 1 to 6 nucleotides. Common examples include mononucleotide repeats such as A/T repeats and dinucleotide repeats such as CA, GA, or GT repeats.
Because microsatellite regions contain repetitive sequences, they are more prone to replication errors. During normal DNA replication, small insertion or deletion errors may occur in these regions. In healthy cells, these errors are usually corrected by the mismatch repair system.
When the mismatch repair system fails, these errors can accumulate. As a result, the length of microsatellite regions changes. This phenomenon is called microsatellite instability.
The main cause of MSI is deficiency in the DNA mismatch repair system, also known as dMMR.
The mismatch repair system is responsible for identifying and correcting DNA replication errors. Several key proteins are involved in this process, including:
MLH1
MSH2
MSH6
PMS2
When one or more of these mismatch repair genes lose function, DNA replication errors may not be properly corrected. Over time, this can lead to the accumulation of mutations across the genome, especially in highly repetitive microsatellite regions.
This is why MSI is often considered a molecular signature of mismatch repair deficiency.
MSI status is generally classified into different categories based on the level of microsatellite instability detected.
MSI-H means high-frequency microsatellite instability. It indicates that multiple microsatellite markers show instability. Tumors with MSI-H usually have significant mismatch repair deficiency and may carry a higher mutation burden.
MSI-H status is clinically important because it may influence cancer screening strategies, prognosis assessment, and therapy selection.
MSI-L means low-frequency microsatellite instability. It indicates that only a small number of tested microsatellite markers show instability.
In many clinical and research settings, MSI-L may be interpreted differently depending on the testing method, cancer type, and laboratory workflow.
MSS means microsatellite stable. It indicates that no significant microsatellite length changes are detected in the tested markers.
MSS tumors generally do not show the high level of microsatellite instability seen in MSI-H tumors.
MSI testing plays an important role in modern oncology because MSI status can provide valuable biological and clinical information.
MSI testing is commonly used as part of the initial screening process for Lynch syndrome, an inherited cancer predisposition syndrome associated with mismatch repair gene defects.
When a tumor shows MSI-H or dMMR features, additional genetic evaluation may be recommended depending on the clinical context.
MSI status can be associated with different tumor behaviors and clinical outcomes. In certain cancer types, MSI-H tumors may have distinct pathological and prognostic characteristics compared with MSS tumors.
MSI/dMMR status is also relevant to treatment decision-making. In oncology, MSI-H or dMMR tumors may respond differently to certain therapies compared with microsatellite stable tumors.
As precision medicine continues to develop, MSI testing has become an important part of molecular tumor profiling.
Beyond clinical diagnostics, MSI testing is also important in cancer research, biomarker discovery, drug development, and molecular assay validation.
Reliable MSI analysis depends not only on the testing platform but also on the quality of controls and reference materials used in the workflow.
Several methods are used to detect MSI or mismatch repair deficiency. The most common approaches include immunohistochemistry, PCR-based fragment analysis, and next-generation sequencing.
Immunohistochemistry, or IHC, is used to evaluate the expression of mismatch repair proteins in tumor tissue samples.
The commonly tested proteins include MLH1, MSH2, MSH6, and PMS2. If one or more of these proteins are absent, the tumor may be classified as mismatch repair deficient.
IHC does not directly measure microsatellite length changes. Instead, it detects the presence or absence of MMR protein expression. Because dMMR is closely related to MSI-H, IHC is widely used as a practical screening method.
PCR-based MSI testing directly analyzes microsatellite markers to determine whether their lengths have changed.
In a typical PCR workflow, selected microsatellite regions are amplified and analyzed. The microsatellite profiles of tumor samples may be compared with matched normal samples. If instability is detected in multiple markers, the sample may be classified as MSI-H.
Traditional MSI panels have included markers such as BAT-25, BAT-26, D5S346, D2S123, and D17S250. Other commonly used MSI marker panels include mononucleotide markers such as BAT-25, BAT-26, NR-21, NR-24, MONO-27, and related markers.
PCR combined with capillary electrophoresis, often called PCR-CE, remains an important method for MSI analysis because it can provide clear fragment size information for selected microsatellite loci.
Next-generation sequencing, or NGS, has become an increasingly important tool for MSI detection.
Unlike traditional PCR methods that focus on a limited number of markers, NGS can analyze many genomic regions simultaneously. MSI status may be inferred from whole-genome sequencing, whole-exome sequencing, targeted gene panels, or other sequencing datasets.
NGS-based MSI detection can be integrated into broader cancer genomic profiling workflows. This makes it useful for laboratories that already perform tumor sequencing for mutation detection, biomarker analysis, or treatment-related genomic profiling.
However, NGS-based MSI testing requires careful assay validation, appropriate bioinformatics pipelines, and reliable reference materials to ensure consistent performance.
MSI testing must be accurate, reproducible, and consistent. This is especially important for clinical laboratories, IVD manufacturers, sequencing service providers, and research laboratories developing or validating MSI assays.
MSI reference standards are materials with known MSI status. They can be used to evaluate whether a testing method can correctly identify MSI-H, MSS, or other MSI-related sample types.
Reference standards are useful for:
Assay development
Analytical validation
Limit of detection evaluation
Quality control
Inter-run reproducibility assessment
PCR-CE workflow verification
NGS panel validation
Bioinformatics pipeline evaluation
Laboratory training
Using well-characterized MSI reference standards helps laboratories reduce uncertainty and improve confidence in MSI testing results.
CB-Gene provides MSI reference standards designed to support molecular diagnostic assay development and validation.
The CB-Gene MSI Reference Standard product includes paired genomic DNA samples, with one sample derived from tumor material and the other from paired or reference normal material. These reference standards include both microsatellite stable and MSI-H sample types.
The standards are confirmed using PCR-CE assay and NGS assay, making them suitable for laboratories working with different MSI testing platforms.
According to CB-Gene MSI Reference Standard product information, the PCR-CE MSI analysis system includes multiple nucleotide markers such as BAT-25, BAT-26, MONO-27, NR-21, NR-24, and NR-27 for MSI typing.
These reference materials can help laboratories verify whether their MSI detection workflow can correctly distinguish MSI-H samples from MSS samples.
MSI reference standards are valuable for a wide range of users in the molecular diagnostics and oncology testing field.
Clinical laboratories can use MSI standards for method validation, routine quality control, and workflow monitoring.
Companies developing MSI detection kits or cancer diagnostic assays can use reference standards to support product development and analytical performance evaluation.
Sequencing laboratories can use MSI reference materials to validate targeted panels and bioinformatics algorithms for MSI calling.
Research teams can use MSI standards to evaluate experimental workflows, compare detection methods, and support translational cancer research.
Microsatellite instability is an important molecular biomarker caused mainly by mismatch repair deficiency. MSI testing is widely used in cancer diagnostics, Lynch syndrome screening, prognosis evaluation, and treatment decision-making.
Common MSI detection methods include IHC, PCR-CE, and NGS. Each method has its own advantages and application scenarios. Regardless of the testing platform, reliable reference standards are essential for assay validation, quality control, and consistent performance.
CB-Gene MSI Reference Standards provide well-characterized MSI-H and MSS genomic DNA materials to support PCR-CE and NGS-based MSI testing workflows. For laboratories and diagnostic developers, these standards can help improve confidence in MSI assay development and validation.
