Frequent allelic imbalances including loss of heterozygosity (LOH) and microsatellite instability (MI) on the long arm of chromosome 21 (21q) have been found in several types of human cancer. This study was designed to identify tumor suppressor locus (or loci) associated with oral squamous cell carcinoma (SCC) on 21q. Among 38 patients with oral SCC tested, 15 (44%) of 34 informative cases showed LOH at one or more loci. Deletion mapping of these 15 tumors revealed three discrete commonly deleted regions on the chromosome arm. A minimal region with frequent LOH was found at the marker D21S236 mapped on 21q11.1. Another region of frequent deletion was identified between markers D21S11 and D21S1436 on 21q21, and a further commonly deleted region was found at D21S1254 on 21q22.1. In addition, we have detected MI on the chromosome arm in our oral SCC samples with significant correlation with tumor stage. Thus, our results strongly suggest that allelic imbalances on 21q may be involved in the development of oral SCC; and that at least three different putative tumor suppressor genes contributing to the pathogenesis of this disease are present on 21q.

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