Characterization of chromosome aberrations in salivary gland tumors by FISH, including multicolor COBRA-FISH

Fluorescence in situ hybridization (FISH), including COBRA-FISH, was used to characterize 11 salivary gland tumors that had been investigated by banding analysis. Five cases were pleomorphic adenoma (PA), three were adenoid cystic carcinoma, and one case each was mucoepidermoid carcinoma, carcinoma ex-pleomorphic adenoma (CaPA), and adenocarcinoma. All 11 cases were selected on the basis that they had shown rearrangement of 6q or 9p or had unresolved aberrations after karyotyping. The COBRA-FISH and FISH analyses led to a revised karyotype in all informative cases and made it possible to clarify almost all chromosomal rearrangements occurring in the tumors. Of particular note were the confirmation of the existence of 6q deletions, a common change in salivary gland carcinomas, and the demonstration that a seemingly balanced t(6;9) resulted in del(6q). Other rearrangements that were revealed by FISH included amplification of 12q sequences (MDM2 and CDK4) in one PA. We also investigated the status of the PLAG1 gene in four cases (one PA, one CaPA, one adenoid cystic carcinoma, and one mucoepidermoid carcinoma) with 8q12 rearrangements. Only in the former two cases were the FISH results compatible with intragenic rearrangements. Overall, the results of the study show that, even with good banding quality and in karyotypes of modest complexity, much new information will be gained by supplementing the banding analysis with a multicolor FISH approach, such as COBRA-FISH.