DETERMINATION OF THE REPLICATION ERROR PHENOTYPE IN HUMAN TUMORS WITHOUT THE REQUIREMENT FOR MATCHING NORMAL DNA BY ANALYSIS OF MONONUCLEOTIDE REPEAT MICROSATELLITES

Microsatellite instability (MI) characterizing tumors with replication errors (RER+ tumors) was first described in colorectal tumors from he reditary non-polyposis colorectal cancer (HNPCC) patients as well as i n sporadic cases. It has also been observed in subgroups of extracolon ic sporadic tumors, but there is no consensus as to the number of micr osatellite loci to examine, and the threshold percentage of unstable l oci required to classify a tumor as RER+. We have recently shown that BAT-26, a mononucleotide repeat microsatellite, was quasi-monomorphic in DNA from normal individuals and from colorectal RER-samples, and sh owed important size variations in RER+ samples. In the present work, w e analyzed BAT-26 allelic profiles in tumors of the breast (n = 107), brain (n = 78), stomach (n = 59), prostate (n = 49), esophagus (n = 36 ), thyroid (n = 31), endometrium (n = 12), and cervix (n = 10) whose R ER status was already known, thus extending BAT-26 analysis to a total of 542 human solid tumors. BAT-26 alleles were quasi-monomorphic in R ER-samples (475/481) and shortened in RER+ tumors (57/61), including f our tumors shown to have been misclassified on the basis of dinucleoti de repeat microsatellite analysis. In 3/481 RER- and 4/61 RER+ cases, BAT-26 size variation was important enough to attract attention, but n ot sufficient to establish the RER status of the corresponding tumors. In these cases, the analysis of BAT-25 and BAT-34C4, two other mononu cleotide repeat microsatellites, was necessary to resolve the ambiguit y. There were only 3 false positive cases. In conclusion, BAT-26 was a ble to identify the RER status of 539 out of 542 tumors from various o rigins (99.5% efficiency) in a single-step experiment without the requ irement for matching normal DNA. (C) 1998 Wiley-Liss, Inc.