Certain populations are known to have a higher prevalence of founder mutations, including, but not limited to, French Canadians, Icelanders, African Americans, and Ashkenazi Jews. Lynch syndrome-causing mutations are found in approximately 3% of all diagnosed colorectal cancers, and 1.8% of all diagnosed endometrial cancers. The average age of diagnosis of cancer in patients with this syndrome is 44 years old, as compared to 64 years old in people without the syndrome. Terminology
Henry T. Lynch, Professor of Medicine at Creighton University Medical Center, characterized the syndrome in 1966. In his earlier work, he described the disease entity as "cancer family syndrome." The term "Lynch syndrome" was coined in 1984 by other authors; Lynch named the condition HNPCC in 1985. Since then the two terms have been used interchangeably, until later advances in the understanding of the genetics of the disease led to the term HNPCC falling out of favor.Other sources reserve the term "Lynch syndrome" when there is a known DNA mismatch repair defect, and use the term "familial colorectal cancer type X" when the Amsterdam criteria are met but there is no known DNA mismatch repair defect. The putative "type X" families appear to have a lower overall incidence of cancer and lower risk for non-colorectal cancers than families with documented DNA mismatch repair deficiency. About 35% of people who meet Amsterdam criteria do not have a DNA-mismatch-repair gene mutation.Complicating matters is the presence of an alternative set of criteria, known as the "Bethesda Guidelines."
Age-based testing for IHC has been suggested in part due to cost-benefit analyses, whereas universal testing for all people with colorectal cancer ensures people with Lynch Syndrome are not missed. To address the costs, researchers are trying to predict MSI or IHC directly from the way the tumor looks under the microscope, without doing any molecular testing. Microsatellite Instability
Mutations in DNA mismatch repair systems can lead to difficulty transmitting regions within the DNA which contain repeating patterns of two or three nucleotides (microsatellites), otherwise known as microsatellite instability (MSI). MSI is identified through DNA extraction from both a tumor tissue sample and a normal tissue sample followed by PCR analysis of microsatellite regions. MSI analysis can be used to identify people who may have Lynch syndrome and direct them for further testing. Classification
Three major groups of MSI-H (microsatellite instability – MSI) cancers can be recognized by histopathological criteria:
right-sided poorly differentiated cancers
right-sided mucinous cancers
adenocarcinomas in any location showing any measurable level of intraepithelial lymphocyte (TIL)The histopathological criteria are not sensitive enough to detect MSI from histology but researchers are trying to use artificial intelligence to predict MSI from histology.In addition, HNPCC can be divided into Lynch syndrome I (familial colon cancer) and Lynch syndrome II (HNPCC associated with other cancers of the gastrointestinal tract or reproductive system).