DIAGNOSTIC USE OF MICROSATELLITE INSTABILITY IN HEREDITARY NONPOLYPOSIS COLORECTAL-CANCER

50 families with a history of colorectal cancer were divided according to whether criteria for hereditary non-polyposis colorectal cancer (H NPCC) were fulfilled totally (A, n=19) or partly (B, n=31) and stratif ied by the demonstration that at least half the cancers tested per fam ily were positive for DNA replication errors (RER+). Accepted clinical and pathological characteristics of HNPCC were found to cluster withi n 12 A/RER+ families in which the mean number of affected individuals per family was 10 . 1. Reliance upon clinical data alone may result in over-diagnosis of HNPCC, in small families who just meet the minimum criteria, whereas underdiagnosis is rare. The criteria could be refine d by inclusion of RER status.