Instability at dinucleotide and trinucleotide repeats in breast cancer

We analyzed 7 mono-, 6 di- and 2 trinucleotide repeat loci in a well characterized series of 69 breast cancer cases, treated in the period 1985-1986 and followed for 12 years. Tumor-associated allele contractions or expansions were observed only at di- and trinucleotide repeats, and were detected in 14/69 cases (20%), of which 7 (10%) showed instability at 2 or more loci (10%). No alterations were detected at mononucleotide repeats known to be unstable in gastrointestinal tumors with the microsatellite mutator phenotype. Disease-free survival at 5 years, overall survival at 12 years of follow-up, tumor stage, estrogen/progesteron receptor status, and expression of the Ki-67 proliferation marker were independent of microsatellite status.