Colorectal cancer (CRC) incidence and mortality are constantly decreasing, but CRC still remains the third most prevalent
cancer and the third most common cause of
cancer death in both males and females in the United States. Recent rapid declines in CRC incidence rates have largely been attributed to increases in screening that can detect and remove precancerous
polyps, and the decrease in death rates for CRC largely reflects improvements in early detection, treatment and the understanding of molecular/genetic basis of CRC. One of the important molecular/genetic findings is the presence of
microsatellite instability (MSI) in
CRCs. Many studies have shown the importance of MSI testing in diagnosing
Lynch syndrome and predicting prognosis and response to chemotherapeutic agents in
CRCs. Increased emphasis has been placed on the importance of MSI testing for all newly diagnosed individuals with
CRCs. Both immunohistochemical staining (IHC) and polymerase chain reaction (PCR)-based MSI testing show high sensitivity and specificity in detecting MSI. The current clinical guidelines and histopathology features are indicative of, but not reliable in diagnosing
Lynch syndrome and
CRCs with MSI. Currently, there are evidences that universal testing for MSI starting with either IHC or PCR-based MSI testing is cost effective, sensitive, specific and is getting widely accepted.