A subgroup of pleomorphic adenomas of the salivary glands is characterized by apparently normal stemline karyotypes. In this investigation we have used FISH to study whether clonal translocations involving chromosomes 8 and 12 might have escaped detection with conventional cytogenetic analysis. Whole chromosome painting probes for chromosomes 8 and 12 were hybridized to interphase nuclei from 22 cytogenetically normal pleomorphic adenomas. In 20 of the 22 cases the majority of the nuclei (75-93%) showed two hybridizing chromosome 8 and chromosome 12 domains of equal size, indicating the presence of two intact copies of each of these chromosomes. Evidence of clonal translocations was only detected in two tumors. These findings show that in the vast majority of adenomas with a normal karyotype we can exclude the possibility of an abnormal non-dividing or very slow growing, and thus undetected, tumor cell population in vitro. Our data provides further evidence to support the existence of a subgroup of pleomorphic adenomas with a normal karyotype.

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