By: Vivian Yuen

A key investigation is whether microsatellite instability in our human genome (all the DNA in the body) can be used to screen for colon cancer. To clarify, a microsatellite is a short sequence of DNA that repeats throughout the genome. Microsatellite instability is a mutation (a change in a DNA sequence that can cause a wrong protein to form) in this short sequence of DNA that cannot be repaired.

Microsatellite instabilities play a relatively significant role in the development of colon cancer. In fact, about 15% of colorectal cancer cases have microsatellite instabilities. The rather prevalent appearance of microsatellite instabilities in both hereditary (passed on through family linkage) and sporadic (not passed on through family linkage) colon cancer shows that they can affect a wide range of cancer cases.

Even more so, the amount of microsatellite instabilities (low, medium, and high) can affect the development of the tumor and determine the effectiveness of a cancer treatment. For example, patients with Lynch Syndrome, a form of colorectal cancer that consists of tumors with high levels of microsatellite instabilities, might have the ability to respond well to chemotherapy, but many studies currently state that patients with tumors with high levels of microsatellite instabilities may not need chemotherapy, due to the low levels of tumor metastasis (tumor metastasis involves tumors spreading from the origin and growing in other parts of the body). Furthermore there is indication that in patients with high levels of microsatellite instabilities, survival rates are higher when using surgery treatment alone (rather than using both surgery and chemotherapy treatment). Additionally, patients with stage 2 colon cancer may exhibit a higher microsatellite instability than do patients with stage 3 colon cancer. As a result, patients with stage 2 colon cancer may show a resistance to chemotherapy. Logically, patients with stage 3 colon cancer may respond better to chemotherapy treatments.  

Testing to determine whether your case of colorectal/colon cancer involves microsatellite instability and whether you have Lynch Syndrome is encouraged. In one test, pathologists take a colorectal polyp sample and a healthy cell sample, and run the samples through a process called the Polymerase Chain Reaction, which allows scientists to get large amounts of a desired DNA sequence. Polymerase Chain Reaction enables scientists to determine the presence of a mutation in the patient’s DNA. Another type of test is using antibodies against a mismatch repair protein (which is not functional in colon cancer cases with microsatellite instability) in order to determine the location of a microsatellite instability. It is crucial to test for microsatellite instabilities because doing so can allow physicians to determine which treatments will best enhance chances of survival.

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