Dr. Nixon on the Role of MSI in Cancer

Andrew B. Nixon, PhD, ​MBA, director, Phase 1 Biomarker Laboratory, associate professor of medicine, Duke University School of Medicine, discusses the role of microsatellite instability (MSI) in cancer.

MSI describes an accumulation of mutations in the telomere region of the chromosome, says Nixon. These mutations represent insertions or deletions, also known as tandem repeats.

Tandem repeats are measurable and occur in ​the DNA when nucleotide pattern repetitions are near one another​, Nixon says.

Notably, a large number of mutations or alterations is in this region of the chromosome, the tumor is deemed microsatellite ​instable, ​says Nixon. This instability is due to a functional loss of DNA mismatch repair (MMR) enzymes.

Although these consist of many proteins, ​MLH1, MSH2, MSH6, and PMS2 are looked at most closely. ​Moreover, an alteration in these MMR proteins results in an MSI phenotype, Nixon concludes.