THE INCIDENCE OF MICROSATELLITE INSTABILITY AND LOSS OF HETEROZYGOSITY IN FIBROADENOMA OF THE BREAST

A majority of studies have shown an increase in the risk of breast can cer among women previously diagnosed with fibroadenoma (FA). At presen t there is conflicting evidence whether Some of the chromosome abnorma lities frequently found in breast carcinoma, such as loss of heterozyg osity (LOH), are already present in FAs and other types of benign brea st disease and, if present, whether such abnormalities are associated with the observed increase in risk. Microsatellite instability (MSI) i s also recognised as a marker of genetic damage and is thought to occu r when there has been damage to the cell's mismatch repair (MMR) syste m. We have analysed 39 cases of FA obtained from paraffin-embedded tis sue for the presence of MSI and LOH at 11 loci to determine if these t ypes of genetic alterations occur in FA. The incidence of MSI and LOH found were 4 of 395 (1.0%) and 5 of 271 (1.8%) informative loci tested respectively. Approximately 8% of cases were positive for MSI and 10% were positive for LOH, with one specimen having multiple occurences o f both MSI and LOH. We conclude that these forms of genetic alteration do occur in FAs but that the incidence is low.