Nonsyntenic Amplification of MYC with CDK4 and MDM2 in a Malignant Mixed Tumor of Salivary Gland

Karyotypic analysis of a metastatic malignant mixed tumor of the salivary gland revealed the presence of double minute chromosomes (dmin), indicative of gene amplification. Comparative genomic hybridization analysis of DNA extracted from the primary and a renal metastasis indicated overt amplification of DNA sequences derived from 8q23–24 and 12q13–15 regions. Subsequent Southern blot analysis of tumor DNA from the metastasis with the use of probes previously mapped to those regions indicated amplification of MYC at 8q23–24 and CDK4 and MDM2 at 12q13–15. Fluorescence in situ hybridization of differentially labeled MYC and MDM2 genes hybridized to tumor metaphase chromosomes revealed an independent nonsyntenic amplification of MYC and MDM2 on dmin in this tumor.