Microsatellite Instability MSI PCR (MSI PCR) Test
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About 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
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To screen cancer patients for genetic mutations that causes Lynch syndrome
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To evaluate the prognosis of colorectal cancer that is not inherited but arise by chance
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To determine the eligibility of cancer patients for immunotherapy
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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
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Bloody stool
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Pain in the abdomen
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Bloating and fullness
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Unexplained diarrhea
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Unexpected weight loss
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Excessive tiredness
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Vomiting
Test preparation
You don't need to prepare in advance to take the microsatellite instability testing. You can eat or drink as usual.
Interpretation of the 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 on Microsatellite Instability(MSI) by PCR Test
Microsatellite instability testing is recommended for individuals diagnosed with colorectal or endometrial cancer, and for colorectal cancer patients with MSI to screen for Lynch syndrome.
No, MSI testing is not intended to detect all cancers. It is used specifically for cancers associated with microsatellite instability or Lynch syndrome.
Along with MSI testing, doctors may recommend immunohistochemistry testing for mismatch repair proteins, genetic testing for Lynch syndrome–related gene mutations, and procedures such as colonoscopy or imaging studies to assess disease extent.
The preferred sample is surgically removed tumor tissue containing both tumor and normal cells. Biopsy samples are generally not suitable for this test.
MSI-High status is often associated with a better prognosis in colon cancer. Such tumors respond well to immunotherapy, have a lower chance of recurrence, and are more easily recognized by the immune system. Your doctor will guide further treatment decisions.
Microsatellite Instability MSI PCR (MSI PCR) Test
