Detection of hidden structural rearrangements by FISH in pleomorphic adenomas

t(3;8) as the sole chromosomal abnormality in a myoepithelial carcinoma ex pleomorphic adenoma: a putative progression event

BACKGROUND

Carcinoma ex pleomorphic adenoma (Ca ex-PA) is defined as a carcinoma arising from a primary (de novo) or recurrent benign pleomorphic adenoma (PA).

METHODS

We present a parotid myoepithelial carcinoma ex pleomorphic adenoma in a 38-year-old man with a t(3;8)(p21;q13) as the only chromosomal alteration by cytogenetic and spectral karyotypic analysis (SKY).

RESULTS

The finding of this translocation in a subset of PA and in the present case suggests a critical role for this event in the malignant transformation of PA.

CONCLUSIONS

Collectively, both the cytogenetic and the molecular studies suggest the concept that PA lacking alterations pursue a benign behavior, whereas those with the t(3;8) translocation may progress to carcinoma.

Cytogenetic analysis of a primary salivary gland myoepithelioma

Myoepithelioma, a rare benign salivary gland neoplasm, is a tumor composed entirely of myoepithelial cells. Unlike pleomorphic adenoma, these tumors lack any ductal epithelial differentiation, and manifest a minor stromal element. Previous cytogenetic and molecular genetic studies have mainly investigated pleomorphic adenomas and reported recurring specific chromosomal alterations at 8q12 and 12q13-q15 regions. The cell origin of these alterations, however, remains speculative. We report the cytogenetic analysis of a parotid myoepithelioma and discuss the putative origin for the cells with cytogenetic alterations. Our analysis shows 12q12 involved in a translocation with a previously unreported partner (1q), and nonrandom del(9)(q22.1q22.3) and del(13)(q12q22). Our results indicate that the myoepithelial cell is the source of those cells with chromosomal alterations, and that myoepithelioma shares 12q alterations reported in a subset of pleomorphic adenomas.

Concurrent cytogenetic, interphase fluorescence in situ hybridization and DNA flow cytometric analyses of a carcinoma ex-pleomorphic adenoma of parotid gland

We report the cytogenetic, fluorescence in situ hybridization (FISH), and DNA ploidy analyses of a high grade carcinoma ex-pleomorphic adenoma of the submandibular gland. Our overall combined analyses showed a marked DNA aneuploidy and numerical abnormalities involving all chromosomes. Cytogenetic analysis revealed a near tetraploid modal chromosomal number with tetraploid loss of chromosomes Y, 1, 6, 9, 11, 14, 15, 17, and 19-21 and hypertetraploid gain of chromosomes 7, 8, and 22. The structural abnormalities included der(1;14)(q10;q10), del(6)(q15q34), +del(6)(q15q34), +der(8) t(1;8)(q12;q12.2),der(9;19)(q10;q10),add(14)(p11.2),i(20)(q10),der(21) t(8;21)(q11.2;q22.3),+der(21)t(8;21) (q11.2;q22.3). Interphase FISH of the primary and short-term cultured cells using directly labeled pericentromeric probes for chromosomes 6-12, 17, 18, and Y resulted in alterations corresponding to the cytogenetic findings. DNA ploidy analysis of both the primary and cultured tumor cells showed a hyperdiploid stemline with DNA indices of 2.6. The results indicate that: (1) marked numerical, structural chromosomal, and DNA content abnormalities are present in this tumor; and (2) alteration at 8q and 6q regions, together with previous results, suggest an association between these events and the development and/or progression of this tumor.

Multiple unrelated translocations in a metastatic epimyoepithelial carcinoma of the parotid gland

We report the cytogenetic, fluorescence in-situ hybridization (FISH) and DNA flow cytometric analysis of a rare metastatic epimyoepithelial carcinoma of the parotid gland to the lung with a clinical course of 29 years. DNA content and FISH analyses of tumor and short-term culture cells showed diploid DNA content and lack of numerical chromosomal abnormalities. Immunohistochemical analysis of the short-term culture cells showed predominantly keratin positive and sparse desmin staining supporting an epithelial rather than myoepithelial origin. Cytogenetic analysis showed 46,XY karyotype with clonal translocations of t(3;22)(q13.2;q13.1), t(1;7)(q21;q22), t(8;9)(p10;p10), and t(5;6) (q35;q21). Our findings indicate that these alterations developed in a diploid stemline during tumor progression and in the epithelial component of this tumor.

Microsatellite Alterations at Chromosome 8q Loci in Pleomorphic Adenoma

OBJECTIVE: To determine the extent, localization, and clinical significance of microsatellite loci alterations at sites of reported cytogenetic abnormalities in pleomorphic adenomas.

BACKGROUND: Pleomorphic adenoma is a benign salivary gland tumor with a propensity for recurrence and potential for malignant conversion. Although its cause remains unclear, clonal cytogenetic abnormalities have been reported consistently.

DESIGN: DNA extracted from paired normal and tumor tissue specimens from 1 patient with carcinoma ex pleomorphic adenoma and 17 patients with pleomorphic adenoma (3 contained foci of carcinoma ex pleomorphic adenoma) was evaluated for loss of heterozygosity at microsatellite loci with a multiplex polymerase chain reaction-based analysis. Correlation with clinical and pathologic features was performed.

RESULTS: Overall 10 (56%) of 18 cases manifested loss of heterozygosity at the loci tested. The frequency of loss of heterozygosity noted on 3p, 6q, 8p, 8q, and 12q microsatellite loci was 17%, 12%, 8%, 47%, and 27% of informative cases, respectively. Specimens from patients with carcinoma ex pleomorphic adenoma showed a similar loss of heterozygosity incidence at these loci. No apparent association between molecular abnormalities and clinical-pathologic features was observed in this cohort.

CONCLUSIONS: Loss of heterozygosity at microsatellite loci on 8q, a breakpoint at which translocations have been previously documented in pleomorphic adenoma, is a frequent event in this tumor. The incidence is not increased in patients with focal carcinoma ex pleomorphic adenoma, suggesting that loss of heterozygosity at 8q is an early event in tumorigenesis. Further evaluation at these loci is needed to identify potential tumor suppressor genes that may be associated with the initiation and progression of pleomorphic adenomas.

Chromosomal and DNA ploidy characterization of salivary gland neoplasms by combined FISH and flow cytometry

Concurrent DNA ploidy by flow cytometry and interphase FISH analysis of chromosomes 6 through 12, 17, 18, X, and Y were prospectively performed on 22 salivary gland neoplasms (four benign and 18 malignant) to investigate the diagnostic and biological implications of their alterations in these neoplasms. Our results show that benign neoplasms lack DNA aneuploidy and numerical chromosomal abnormalities. Low-grade malignant neoplasms, except for two lesions, manifested small chromosomal gains and losses and were generally DNA diploid or near-diploid aneuploid, whereas all high-grade tumors showed marked polysomy and were DNA aneuploid. Marked intratumoral and intertumoral chromosomal heterogeneity also were noted in and between individual tumors. Although polysomy was the main finding in DNA aneuploid lesions, monosomy was more noted in DNA diploid neoplasms and was restricted to chromosomes 8, 11, and 17. Significant correlation between the DNA index, chromosomal aneusomy, histological grade, and tumor stage was noted. Our study indicates that (1) benign salivary gland neoplasms lack gross DNA content and numerical chromosomal abnormalities, (2) clonal chromosomal alterations are manifested in most DNA diploid and all DNA aneuploid malignant tumors, (3) chromosomal gain is the most common alteration; chromosomal loss is less frequent and restricted to certain chromosomes, and (4) DNA aneuploidy and chromosomal aneusomy characterize tumors with aggressive features.

Genotypic alterations in benign and malignant salivary gland tumors: histogenetic and clinical implications

Loss of heterozygosity (LOH) and microsatellite instability (MI) were examined at 24 microsatellite loci in 46 primary benign and malignant salivary gland tumors. Among the 27 benign tumors, 11 (40.7%), manifested microsatellite alterations in at least one locus; of these, five (18.5%) showed LOH and four (14.8%) had microsatellite instability at two or more loci. Four of 11 pleomorphic adenomas (36.4%) had allele loss on the long arm of chromosome 8. Among the 19 malignant neoplasms examined, 10 (52.6%) and one (5.2%) had allele losses and MI, respectively, at multiple loci; three tumors showed MI at only one locus. Frequent LOH was detected at D8S166 (8q11-12), D17S799, and D17S122 (17p-17p11-2) loci, with an incidence of 40%, 37.5%, and 43%, respectively. In general, malignant neoplasms with LOH exhibited aggressive tumor characteristics. Statistically significant correlation's were found between LOH and pathologic classification (chi 2, p = 0.05), higher grade (p = 0.02), DNA aneuploidy (p = 0.005), and a proliferative index of > 6% (p = 0.005) of the malignant tumors. Carcinomas with 17p loci alterations, including two carcinomas expleomorphic adenoma with concurrent 8q LOH, showed more aggressive features. The results suggested that (a) loci on chromosome 8q may harbor a tumor suppressor gene or genes associated with the development or progression of some salivary neoplasms; (b) alterations on the short arm of chromosome 17 may represent an event related to tumor progression; and (c) tumors with LOH at multiple loci have aggressive biologic characteristics.