Microsatellite Instability(MSI) by PCR Test
Microsatellite Instability(MSI) by PCR Test
The Microsatellite Instability (MSI) test is a screening procedure that uses the principles of polymerase chain reaction to look at the stability of the microsatellite region and see if a patient with colorectal or endometrial cancer is at risk for Lynch syndrome or other hereditary cancer syndromes.
Microsatellites, or short tandem repeats, are the sequences of DNA bases that are repeated several times and are susceptible to accumulating harmful changes because of defects in a DNA repair process known as the mismatch repair (MMR) system. If a cell's MMR system isn't working right, errors slowly accumulate, making the microsatellite unstable, which results in the rapid proliferation of tumor cells.
According to the frequency of MSI, tumors are classified into three groups: microsatellite stable (MSS), microsatellite instability-low (MSI-L), and microsatellite instability-high (MSI-H). About 15% of people with colorectal cancer have MSI-H status, with 3–5% of cases linked to Lynch syndrome, also known as hereditary nonpolyposis colorectal cancer syndrome (HNPCC).
Hence, if you are diagnosed with colorectal or endometrial cancer, knowing your MSI status and Lynch syndrome diagnosis is crucial, as this information can help your doctor create a personalized treatment plan for a more effective response.
What is the Microsatellite Instability Testing Used For?
The Microsatellite instability testing is used
To screen cancer patients for genetic mutations that causes Lynch syndrome
To evaluate the prognosis of colorectal cancer that is not inherited but arise by chance
To determine the eligibility of cancer patients for immunotherapy
For predicting patient’s response to immunotherapy
Symptoms of Lynch Syndrome
People with Lynch syndrome usually do not show any symptoms until the disease progresses to advanced stages. But when symptoms appear, they often mimic other colon diseases and include
Bloody stool
Pain in the abdomen
Bloating and fullness
Unexplained diarrhea
Unexpected weight loss
Excessive tiredness
Vomiting
Preparation for Test
You don't need to prepare in advance to take the microsatellite instability testing. You can eat or drink as usual.
Interpretation of Test Results
Based on the presence or absence of unstable markers, the interpretation of microsatellite instability test results are provided in the table below:
|
MSI Results |
Interpretation |
|
Instability in two or more markers
|
MSI- High (MSI-H) Genetic testing and counseling for Lynch syndrome needed |
|
Instability only in one marker |
MSI- Low (MSI-L) Genetic testing and counseling for Lynch syndrome needed |
|
All markers are unaltered |
MSI- Stable (MSI-S) Presence of Lynch syndrome is unlikely |
FAQs
Who should take microsatellite instability testing?
Microsatellite instability testing is recommended for individuals diagnosed with colorectal or endometrial cancer, as well as for colorectal cancer patients with MSI to screen for Lynch syndrome.
Can MSI testing detect all types of cancers?
No, MSI testing is not meant to detect all types of cancers. Instead, it is used to screen people with cancers that exhibit microsatellite instability or are associated with Lynch syndrome.
Are there any other tests I must take with MSI testing?
Along with MSI testing, your doctor may recommend additional tests such as immunohistochemistry (IHC) testing for mismatch repair proteins in the tumor, genetic testing to identify mutations in the genes associated with Lynch syndrome, and colonoscopy or other imaging studies to evaluate the extent of the disease.
What kind of sample is used in MSI testing?
The preferred sample in this Test is the surgery-removed tumor tissue, which consists of both the tumor and normal cells. In this regard, the biopsy material is not appropriate.
My result indicates MSI-High. What should I do?
Having MSI-High status may not necessarily be a bad thing if you are diagnosed with colon cancer, as your immune system can readily identify and target MSI-high tumors. It is for this same reason that people with MSI -High cancer respond well to immunotherapy and have a better outlook than other forms of colon cancer. Also, they are less likely to experience a recurrence.
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