Lynch syndrome, also known as hereditary nonpolyposis colorectal cancer (HNPCC), is the most common cause of hereditary colorectal cancer and is caused by a germline mutation in one of the genes within the DNA mismatch repair (MMR) system. In most cases, it is most effective to first evaluate suspected Lynch syndrome with immunohistochemistry (IHC) or polymerase chain reaction (PCR) testing, as only 2-4% of colorectal cancers are Lynch syndrome associated. However, if strong suspicion exists, it is reasonable to proceed with genetic testing.
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