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A National Cancer Institute Workshop on Hereditary Nonpolyposis Colorectal Cancer Syndrome: meeting highlights and Bethesda guidelines.

Hereditary nonpolyposis colorectal cancer (HNPCC) is a distinct autosomal dominant syndrome accounting for approximately 5%–6% of the total colorectal cancer burden with clinical and pathologic features caused by defective mismatch repair genes(1). Germline mutations in hMSH2, hMLH1, hPMS1, hPMS2, and MSH6/GTBP have been identified in affected individuals(2,3).HNPCC is characterized by early-onset colorectal cancer (median age at diagnosis 45 years); right-sided predominance; excess synchronous and metachronous colorectal neoplasms; and an increased incidence of extracolonic neoplasms, including endometrial, small-bowel, gastric, renal pelvis and ureter, and ovarian tumors and skin lesions, such as sebaceous adenomas, carcinomas, and keratoacanthomas (4–10). In 1991, the International Collaborative Group on Hereditary Nonpolyposis Colorectal Cancer (11) established minimal clinical criteria for recruiting HNPCC patients for collaborative studies. These criteria, also known as the Amsterdam Criteria, include the following: 1) at least three relatives with histologically verified colorectal cancer, one of them a first-degree relative of the other two (familial adenomatous polyposis excluded); 2) at least two successive generations affected; and 3) in one of the individuals, diagnosis of colorectal cancer before the age of 50. These criteria were pivotal in identifying kindreds that eventually led to the association of the HNPCC syndrome with germline mismatch repair gene mutations (MMR). However, the criteria do not account for extracolonic cancers or for small kindreds. On November 11 and 12, 1996, the Early Detection Branch of the National Cancer Institute convened an international workshop in Bethesda, MD, entitled ‘‘The Intersection of Pathology and Genetics in the Hereditary Nonpolyposis Colorectal Cancer (HNPCC) Syndrome.’’ The purpose of the workshop was to clarify the role of genetics in the pathology of HNPCC. Discussions centered on genomic instability, multistep carcinogenesis and the role of mismatch repair genes in HNPCC, histopathology of HNPCCs and possible relationships to molecular genetic changes, markers of cell proliferation and their relationship to HNPCC as well as their potential use in early diagnosis and prognosis, and, lastly, clinicopathologic criteria that could lead to the identification of additional HNPCC patients. The keynote speaker was Dr. Alfred Knudson (Fox Chase Cancer Center, Philadelphia), who discussed the tumor spectrum of the HNPCC syndrome. Issues that arose during the workshop are discussed below.