et al cancer res 59 1 300 303 1997 this sample was monomorphic for all five mononucleotide repeats used in this study suggesting that it was misclassified with dinucleotide repeats possibly due to the fact that germline dna did not match with tumour dna in table ii and fig3 these 6 samples were considered as mss of 55 colon and gastric tumours and cell lines previously classified as mss and containing data for all 5 repeats 53 96 4 were monomorphic at all 5 markers one tumour was monomorphic at 4 markers 2 and 1 tumour was monomorphic at 3 5 2 repeats none of the 55 mss tumours showed allelic shifts in 3 or more repeats fig3 still complying with the msi identification criteria of 2 5 repeat polymorphisms described earlier these results are illustrated by fig3 which shows the percentage of samples with allelic size shifts in the five mononucleotide repeats in caucasian germline dna u25a1 african germline dna u25aa mss tumours msi h colorectal tumours and msi h gastric tumours the three mononucleotide repeats nr21 nr22 and nr24 are quasimonomorphic in germline dna and similar to bat 25 and bat 26 are highly sensitive to somatic deletion in msi h tumours distinction of msi h from mss tumours is unambiguous when these three.