Deletions of chromosome 5(q22-23, q32-33) and t(10;12) (p15;q14-15) with 12q breakpoint at the 5' of the HMGIC and translocation of the entire gene to the 10 marker chromosome followed by deletion/amplification of the segment containing HMGIC and MDM2 genes have been reported {653,1220,2193}. Rearrangements of 8q12 are a frequent finding. Alterations at 12q 13-15 with amplification of HMGIC and MDM2 genes have also been reported {2125}. Cytogenetic evidence of amplification (homogeneously stained region and double minute) was found in 40% of these tumours. Both genes may contribute to the malignant transformation of pleomorphic adenoma. Alterations at chromosomes 6q deletion and 8q rearrangements have been reported.

Molecular genetics

Microsatellite analysis of these tumours has shown LOH at chromosome 8q and 17p. Concurrent analysis of the benign and malignant components of these tumours showed 8q and/or 12q in both components and additional alterations in 17p only in the carcinoma {651}. In another study homozygous deletion of the p16 gene on chromosome 9p21 was found in carcinoma of one case and microsatellite instability was noted in both the adenoma and carcinoma components in two tumours {2510}. A single case report of a carcinosarcoma, in which the carcinoma and the sarcoma components were concurrently analyzed, showed lack of p53 alterations and concomitant LOH at different loci on chromosome 17 and 18 supporting mon-oclonality {932}.

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