Hereditary nonpolyposis colorectal cancer (HNPCC)/Lynch syndrome

Hereditary nonpolyposis colorectal cancer HNPCC, Lynch syndrome) is a genetic disease of autosomal dominant inheritance. It is caused by a mutation in one of four genes of the DNA mismatch repair system and confers a markedly increased risk for various types of cancer, particularly of the colon and the endometrium. Its prevalence in the general population is about 1 in 500, and it causes about 2% to 3% of all colorectal cancers. Lynch syndrome is diagnosed in two steps: If it is suspected (because a patient develops cancer at an unusually young age or because of familial clustering), the tumor tissue is analyzed for evidence of deficient mismatch repair (microsatellite instability, loss of mismatch repair protein expression). If such evidence is found, a genetic mutation is sought. The identification of a pathogenic mutation confirms the diagnosis in the patient and enables predictive testing of other family members. Diagnostic evaluations for Lynch syndrome should be carried out with appropriate genetic counseling.

Selective literature review.

Prospective cohort studies from Germany, Finland and the Netherlands have shown that colorectal cancers detected by systematic colonoscopic surveillance tend to be at an earlier stage than those that are discovered after the patients present with symptoms. The Finnish study also showed an overall reduction in cancer risk from colonoscopic polypectomy at regular intervals.

The studies conducted so far have not yet clearly documented the putative benefit of an individualized, risk-adapted surveillance strategy. Until this is done, patients with Lynch syndrome and healthy carriers of causative mutations should be monitored with annual colonoscopy and (for women) annual gynecological examination.