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, and Lynch himself coined the term HNPCC in 1985. Since then, the two terms have been used interchangeably, until more recent advances in the understanding of the genetics of the disease led to the term HNPCC falling out of favour.
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 patients meeting 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".
Read more about this topic: Hereditary Nonpolyposis Colorectal Cancer