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One of the first successful efforts of the International Collaborative Group on HNPCC (ICG-HNPCC) at its meeting in Amsterdam in 1990 was the establishment of a set of selection criteria for families with hereditary nonpolyposis colorectal cancer (HNPCC, Lynch syndrome) to provide a basis for uniformity in collaborative studies (Table 1).1 Until 1990, such criteria were lacking and the descriptions of the syndrome in the literature varied widely. In the absence of a common nomenclature it was impossible to compare the results of different studies on HNPCC. The wide acceptance of the ICG criteria is reflected by the fact that almost all investigators currently make use of them. However, the criteria have also been criticized. Some investigators feel that the criteria exclude some classic HNPCC families because they do not take into account the extracolonic cancers that are part of the syndrome. There is also concern that the criteria are being used inappropriately for the diagnosis of HNPCC. As criteria for the selection of families for research, they were originally aimed at specificity more than sensitivity. It is now considered that many true HNPCC families would be missed if the criteria are applied to clinical diagnosis, and that families not meeting the criteria might be falsely reassured and excluded from genetic counseling, DNA testing, or surveillance. To resolve these problems, many investigators have developed additional criteria.2–6 At the ninth meeting of the ICG-HNPCC held in Noordwijk, the Netherlands, in 1997, a definition of HNPCC was proposed that was aimed at helping clinicians to identify families. This provided a detailed description of the specific features of HNPCC rather than the rigid criteria required for collaborative studies. In addition, at the ninth meeting, and also at the tenth held in Coimbra, Portugal, in 1998, new selection criteria for collaborative studies were proposed that included the extracolonic cancers associated with HNPCC. Definition of HNPCC

Hereditary nonpolyposis colorectal cancer (HNPCC) dates to Warthin's description of family G, which he began studying in 1895. Warthin's observations were not fully appreciated until 1966 when two families with an autosomal dominant inheritance pattern of nonpolyposis colorectal cancer (CRC) and endometrial cancer were described. This condition was first termed the "cancer family syndrome" and was later renamed HNPCC. Some have proposed that HNPCC consists of at least two syndromes: Lynch syndrome I, with hereditary predisposition for CRC having early (approximately 44 years) age of onset, a proclivity (70%) for the proximal colon, and an excess of synchronous and metachronous colonic cancers and Lynch syndrome II, featuring a similar colonic phenotype accompanied by a high risk for carcinoma of the endometrium. Transitional cell carcinoma of the ureter and renal pelvis and carcinomas of the stomach, small bowel, ovary, and pancreas also afflict some families. Current estimates indicate that HNPCC may account for as much as 6% of the total CRC burden. There are no known premonitory phenotypic signs or biomarkers of cancer susceptibility in the Lynch syndromes. This report will summarize current knowledge, with emphasis on the manner in which this knowledge can be employed effectively for diagnosis and management of HNPCC.

Forty-four asymptomatic putative Lynch syndrome patients participated in a colonoscopy screening program. There were 18 men and 26 women; mean age was 44 yr. Thirty percent of Lynch syndrome patients had at least one adenoma; 20% had multiple adenomas. In 18% of the patients, adenomas were discovered proximal to the splenic flexure. In a reference group of 88 age- and sex-matched patients, 11% had adenomas, 4 % had multiple adenomas, and 1 % had right-sided adenomas. Twenty-one Lynch syndrome patients had follow-up colonoscopies. Of 7 patients with adenomas on initial examinations, 6 had adenomas at follow-up. Of 14 patients with negative initial examination results, 3 had adenomas at follow-up. The prevalence of adenomas in the Lynch syndromes is greater than in an unselected reference group. The adenomas are more proximally located, corresponding to the site of cancer distribution in the Lynch syndromes. A high rate of synchronous and metachronous lesions is found. Our findings support the hypothesis that adenomatous changes are the premalignant lesion in the Lynch syndromes. We also found evidence of heterogeneity among Lynch syndrome families in adenoma incidence.