Specificity and implications of ring chromosomes and dicentrics in benign mixed salivary gland tumours.

Among 61 human pleomorphic adenomas subjected to chromosomal study by banding methods, two rare cases were detected, one having a dicentric marker chromosome and the other a ring chromosome included in the stemline karyotype. Excepting meningiomas, such marker types have previously only been observed in different types of malignant neoplasms. However, as in meningiomas, the occurrence of dicentrics or rings has no implications as regards the question of malignancy. Both our mixed tumours showed structural changes affecting one chromosome No. 8. These findings, along with similar observations in other pleomorphic adenomas, are discussed in relation to recently advanced hypotheses about the role of oncogenes and changes of gene dosage in the genesis and/or development of mixed tumours.