MICROSATELLITE INSTABILITY AND LOSS OF HETEROZYGOSITY IN SQUAMOUS CELL CARCINOMA OF THE HEAD AND NECK

Background. Microsatellite instability (MSI) in head and neck squamous cell carcinoma (HNSCC) has been reported with a wide range of frequencies. The aim of our study was to disclose the frequency and basis of MSI in HNSCC and to corre- late MSI and findings on loss of heterozygosity (LOH) with the clinical data. Methods. We analyzed MSI and LOH in 91 tumors. All tumors presenting instability were analyzed for the expression of mismatch repair genes (MMR) proteins. Results. Low-level microsatellite instability (MSI-L) was seen in 7.7% of the HNSCC. None of the MSI-L tumors had aberrant MMR protein expression. LOH rates up to 57% were identified for different regions on chromosome 3p. For the marker D10S197, we found a significant correlation between LOH and tumor stage IV. Conclusion. Our results indicate that MMR gene inactivation is rare among primary HNSCC. In contrast, the MSI-L phenotype plays a role in a small subset of tumors. LOH on chromosome