Genetics, natural history, surveillance, management, and gene mapping in the Lynch syndrome

Hereditary nonpolyposis colorectal cancer (HNPCC), also termed Lynch syndrome, may account for as much as 10-15 percent of the total colorectal burden. Lynch syndrome I is characterized by site-specific colorectal cancer (CRC) with early (congruent to age 45) onset, predilection to the proximal colon (congruent to 70%), and a marked susceptibility to metachronous CRC (45% following hemicolectomy or segmental resection). Lynch syndrome II shows the same colonic features but includes an excess of extra-colonic CRCs, namely carcinoma of the endometrium, ovary, small bowel, stomach, pancreas and transitional cell carcinoma of the ureter and renal pelvis. These findings form the basis for our surveillance recommendations: full colonoscopy initiated at age 25 and repeated every other year, and, in Lynch syndrome II variant, biannual endometrial aspiration biopsy. Screening for the remaining cancer types is dependent upon the availability of screening modalities and the pattern of cancer expression within specific families. The excess of metachronous CRC mandates that subtotal colectomy be performed for any CRC. The lack of premonitory physical stigmata has forced clinicians to diagnose HNPCC based on the family history in concert with the natural history features of the cancer phenotype within the pedigree. Problems with this approach include variable gene penetrance, the fact that cancer affected may or may not be gene carriers, death of gene carriers prior to developing cancer, and difficulty with pathology verification of tumor site and type. Partial resolution of these problems is possible now that HNPCC has been linked to chromosomes 2p and 3p and the susceptibility gene at chromosome 2p has been cloned.(ABSTRACT TRUNCATED AT 250 WORDS)