Cytogenetic investigations on a cell line derived from a carcinoma arising in a salivary gland pleomorphic adenoma

Salivary Gland Tumors: Current Concepts and Controversies

This current review focuses on current concepts and controversies for select key salivary gland epithelial neoplasms. Rather than the traditional organization of benign and malignant tumors, this review is structured around select key topics: biphasic tumors, mammary analogue secretory carcinoma, and the controversy surrounding polymorphous low-grade adenocarcinoma and cribriform adenocarcinoma of (minor) salivary gland origin.

Molecular Pathology: Predictive, Prognostic, and Diagnostic Markers in Salivary Gland Tumors

Although initial attempts at using ancillary studies in salivary gland tumor classification were viewed with skepticism, numerous advances over the past decade have established a role for assessment of molecular alterations in the diagnosis and potential prognosis and treatment of salivary gland tumors. Many monomorphic salivary tumors are now known to harbor defining molecular alterations, usually translocations. Pleomorphic, high-grade carcinomas tend to have complex alterations that are often further limited by inaccuracy of initial classification by morphologic and immunophenotypic features. Next-generation sequencing techniques have great potential in many aspects of salivary gland tumor classification and biomarker discovery.

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.

Establishment and characterization of pleomorphic adenoma cell systems: an in-vitro demonstration of carcinomas arising secondarily from adenomas in the salivary gland

Background

Among the salivary gland carcinomas, carcinoma in pleomorphic adenoma has been regarded as a representative carcinoma type which arises secondarily in the background of a pre-existent benign pleomorphic adenoma. It is still poorly understood how and which benign pleomorphic adenoma cells transform into its malignant form, carcinoma ex pleomorphic adenoma.

Methods

We have established five cell systems from a benign pleomorphic adenoma of the parotid gland of a 61-year-old woman. They were characterized by immunofluorescence, classical cytogenetics, p53 gene mutational analysis, fluorescence in-situ hybridization, and histopathological and immunohistochemical examinations of their xenografts, to demonstrate their potency of secondary transformation.

Results

We established and characterized five cell systems (designated as SM-AP1 to SM-AP5) from a benign pleomorphic adenoma of the parotid gland. SM-AP1 to SM-AP3 showed polygonal cell shapes while SM-AP4 and SM-AP5 were spindle-shaped. SM-AP1-3 cells were immunopositive for keratin only, indicating their duct-epithelial or squamous cell differentiation, while SM-AP4/5 cells were positive for both keratin and S-100 protein, indicating their myoepithelial cell differentiation. Chromosome analyses showed numeral abnormalities such as 5n ploidies and various kinds of structural abnormalities, such as deletions, translocations, derivatives and isodicentric chromosomes. Among them, der(9)t(9;13)(p13.3;q12.3) was shared by all five of the cell systems. In addition, they all had a common deletion of the last base G of codon 249 (AGG to AG_) of the p53 gene, which resulted in generation of its nonsense gene product. Transplanted cells in nude mice formed subcutaneous tumors, which had histological features of squamous cell carcinoma with apparent keratinizing tendencies. In addition, they had ductal arrangements or plasmacytoid appearances of tumor cells and myxoid or hyaline stromata, indicating some characteristics of pleomorphic adenoma.

Conclusion

This study demonstrates in vitro that certain cell types from pleomorphic adenoma are able to clone and survive over a long term and develop subcutaneous tumors in nude mice. The histological features of squamous cell carcinoma from the transplanted cell systems in nude mice might suggest a secondary onset of malignancy from a pre-existing benign adenoma.

Translocation, deletion/amplification, and expression of HMGIC and MDM2 in a carcinoma ex pleomorphic adenoma

Carcinoma ex pleomorphic adenoma (CexPA) is a carcinoma developing within a pre-existing benign pleomorphic adenoma (PA). Here we describe the identification and characterization of a series of genetic events leading to translocation, deletion/amplification, and overexpression of the HMGIC and MDM2 genes in a CexPA at an early stage of development. The tumor had a pseudodiploid stemline karyotype with a del(5)(q22-23q32-33) and a t(10;12)(p15;q14-15). In addition, there were several sidelines with double minute chromosomes (dmin) or homogeneously staining regions (hsr). Fluorescence in situ hybridization (FISH) mapping revealed that the 12q14-15 breakpoint was located centromeric to HMGIC and that the entire gene was juxtaposed to the der(10) chromosome. Detailed analysis of cells with dmin and hsr revealed that HMGIC and MDM2 were deleted from the der(10) and that the dmin and hsr were strongly positive for both genes. Southern blot analysis confirmed that both HMGIC and MDM2 were amplified and that no gross rearrangements of the genes had occurred. Immunostaining revealed that the HMGIC protein was highly overexpressed particularly in the large polymorphic cells within the carcinomatous part of the tumor. These findings suggest that amplification and overexpression of HMGIC and possibly MDM2 might be important genetic events that may contribute to malignant transformation of benign PA.

Cytogenetic similarities between two types of salivary gland carcinomas: adenoid cystic carcinoma and polymorphous low-grade adenocarcinoma

Adenoid cystic carcinoma (ACC) and polymorphous low-grade adenocarcinoma (PLGA) are low-grade adenocarcinomas of salivary glands with a putative common histogenesis from the intercalated ducts but featuring distinct histological appearances. Hybrid tumors containing areas with histological patterns of both neoplasms have been reported but, to our knowledge, the question of their genotypic similarity has not yet been approached. As part of an ongoing study on cytogenetic characterization of salivary gland tumors, from a group of 24 malignant neoplasms, three out of five cases of ACC and three of four cases of PLGA were selected for their similar karyotypic changes. All of them displayed chromosome 12 abnormalities, affecting the 12q12-q13 region in four (all ACC cases and one PLGA case), 12q22 in one PLGA case, and 12p12.3 in the remaining. From this group of neoplasms, one PLGA and one ACC showed the same t(6;12)(p21;q13). Our findings favor the concept that tumors of salivary glands displaying epithelial and myoepithelial phenotypes share a common histogenesis.

Familial occurrence of acinic cell carcinoma of the parotid gland

We report the familial occurrence of acinic cell carcinoma involving the parotid gland, the first such report of which we are aware. The familial occurrence of any salivary gland neoplasm is rare. Several reports are present in the literature, including pleomorphic adenoma, Warthin tumor, carcinoma of the submandibular gland, and malignant lymphoepithelial lesion. We report the case of a 35-year-old man who underwent excision of a left parotid gland acinic cell carcinoma. Eight years later, his daughter presented at the age of 16 years with a nontender parotid gland mass that was excised and found also to be acinic cell carcinoma. The histologic features of both neoplasms were typical of acinic cell carcinoma. While this may represent a coincidental event, the possibility that this familial occurrence is a manifestation of common genetic or environmental risk cannot be excluded.

In vitro transformation of cell lines from human salivary gland tumors

Explanted cells from salivary gland tumors are particularly difficult to propagate in vitro and not efficiently immortalized by agents such as simian virus 40. Human papillomavirus 16 (HPV16) has been widely used to transform cells of epithelial origin, but its use for salivary gland cell transformation has not been described. In this study, we employed viral constructs containing the E6/E7 genes of HPV16 to infect and stably transform 9 salivary gland tumor cell cultures. Four of the tumor cell cultures were derived from benign tumors and 5 from malignant tumors. All of the original cell cultures were diploid; however, 6 contained subpopulations of cells with structural abnormalities. All 9 cell cultures were successfully transformed, and 8 were immortalized. The resulting cell lines have decreased serum requirements, exhibit a high proliferation rate, are E6/E7-positive and form colonies in soft agar. Immuno-histochemical and molecular studies confirmed that the transformed cells were indeed epithelial/myoepithelial in origin. All of the transformed cell lines had a diploid or near-diploid karyotype, and 2 contained the original translocated chromosomes in all cells. Our report represents a new application of the E6/E7 system in immortalizing salivary gland cell cultures, resulting in retention of the cellular features found in the native tissue without a general destabilization of the karyotype. These types of tissue culture resources should prove useful for positional cloning and functional studies of genes involved in salivary gland oncogenesis.

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.

NAB2, a corepressor of NGFI-A (Egr-1) and Krox20, is induced by proliferative and differentiative stimuli

Previous work had identified a corepressor, NAB1, which represses transcriptional activation mediated by NGFI-A (also known as Egr-1, zif268, and Krox24) and Krox20. These zinc finger transcription factors are encoded by immediate-early genes and have been implicated in a wide variety of proliferative and differentiative processes. We have isolated and characterized another corepressor, NAB2, which is highly related to NAB1 within two discrete domains. The first conserved domain of NAB2 mediates an interaction with the R1 domain of NGFI-A. NAB2 represses the activity of both NGFI-A and Krox20, and its expression is regulated by some of the same stimuli that induce NGFI-A expression, including serum stimulation of fibroblasts and nerve growth factor stimulation of PC12 cells. The human NAB2 gene has been localized to chromosome 12ql3.3-14.1, a region that is rearranged in several solid tumors, lipomas, uterine leiomyomata, and liposarcomas. Sequencing of the Caenorhabditis elegans genome has identified a gene that bears high homology to both NAB1 and NAB2, suggesting that NAB molecules fulfill an evolutionarily conserved role.

Malignant salivary gland neoplasms: a cytogenetic study of 19 cases

A group of 19 malignant salivary gland neoplasms of various histological types (mucoepidermoid carcinoma, acinic cell carcinoma, adenoid cystic carcinoma, epithelial-myoepithelial carcinoma, myoepithelial carcinoma, basal cell adenocarcinoma, carcinoma ex-pleomorphic adenoma, ductal carcinoma, adenocarcinoma not otherwise specified and undifferentiated carcinoma) were cytogenetically investigated. Previous karyotypic information revealed deletion of the long arm of chromosome 6, loss of chromosome Y and the gain of chromosome 8 as the most recurrent deviations found in these neoplasms. Clonal chromosome aberrations were detected in 11 cases of this series. In 7 of them there were only numerical deviations (gain of chromosomes 2, 7, 8, 10 and X and loss of chromosomes 18, 21 and Y) without concomitant structural anomalies. Structural rearrangements such as t(2;7), t(6;16), t(6;9) and t(1;1) translocations were found in two mucoepidermoid carcinomas, one adenoid cystic carcinoma and one ductal carcinoma, respectively. The wide spectrum of changes found in this group of neoplasms may reflect the diversity in their histogenesis and differentiation phenotypes.

Trisomy 8 and 18 as frequent clonal and single-cell aberrations in 185 primary breast carcinomas

For cytogenetic investigations short-term cultures of 185 breast carcinomas (135 invasive ductal, 21 invasive lobular, 12 invasive ductal with intraductal components, seven heterogeneous, six intraductal, four invasive ductal and lobular) were prepared. Cytogenetic examinations revealed clonal abnormalities in 39 cases with a predominance of simple numerical chromosome changes, i.e., trisomies of chromosomes 7, 8, and 18. One hundred forty-six tumors did not show clonal abnormalities, but single-cell aberrations other than monosomies occurred in 79 of these tumors. Compared to cells of epithelial hyperplasia of the breast, amniotic fluid cells, and cells from pleomorphic adenomas cultivated using the same medium, the frequency of single-cell trisomies was significantly higher. Trisomy 8 was not only found as a clonal aberration in 10 cases but was also the most frequent non-clonal aberration. Trisomy 7 and 18 were also frequent clonal as well as non-clonal cytogenetic deviations.

Cytogenetic findings in seven lacrimal gland neoplasms

We have undertaken cytogenetic investigation of seven benign and malignant lacrimal gland neoplasms. This study showed recurrent chromosomal abnormalities involving chromosomes 3, 8, 9, and 12. These features are similar to those found in benign and malignant salivary gland tumors, which suggests possible common mechanisms involved in the neoplastic proliferation of these histologically related tumors.

Serial cultivation of epithelial cells from human and macaque salivary glands

To study the regulation of human salivary-type gene expression we developed cell culture systems to support the growth and serial cultivation of salivary gland epithelial and fibroblastic cell types. We have established 22 independent salivary gland epithelial cell strains from parotid or submandibular glands of human or macaque origin. Nineteen strains were derived from normal tissues and three from human parotid gland tumors. Both the normal and the tumor-derived salivary gland epithelial cells could be serially cultivated with the aid of a 3T3 fibroblast feeder layer in a mixture of Ham's F12 and Dulbecco's modified Eagle's media supplemented with fetal bovine serum, calcium, cholera toxin, hydrocortisone, insulin, and epidermal growth factor. Salivary gland epithelial cells cultured under these conditions conditioned to express the genes for at least two acinar-cell-specific markers at early passages. Amylase enzyme activity was detected in conditioned media from cultured rhesus parotid epithelial cells as late as Passage 5. Proline-rich-protein-specific RNAs were detected in primary cultures of both rhesus and human parotid epithelial cells. Neither amylase enzyme activity nor PRP-specific RNAs were detected in fibroblasts isolated from the same tissues. In addition, salivary gland epithelial cells cultured under our conditions retain the capacity to undergo dramatic morphologic changes in response to different substrata. The cultured salivary gland epithelial cells we have established will be important tools for the study of salivary gland differentiation and the tissue-specific regulation of salivary-type gene expression.

Karyotypic variability and evolutionary characteristics of a polymorphous low grade adenocarcinoma in the parotid gland

The chromosomes of a polymorphous low-grade adenocarcinoma originating from a pleomorphic adenoma of the parotid gland were studied. Three successful preparations were performed. A minor fraction of cells showed normal karyotypes and some cells only inconsistent, usually numerical, deviations. The remaining cells constituted an abnormal monoclonal population with an unusual and very extensive karyotypic variability. The origin of most marker chromosomes could be wholly or partly clarified. Five different subclones could be distinguished on basis of different specific marker chromosomes. The characteristics of the marker sets suggested a closely interrelated derivation of the subclones. The results also provide insight as to the influence of random factors and/or differential growth rate on the chromosomal picture observed in in vitro systems. The present chromosomal observations showed no similarities either to the cytogenetical findings in the five previously reported salivary gland adenocarcinomas or to the deviations seen in the single studied case of carcinoma ex-pleomorphic adenoma.

Mucoepidermoid tumor of the parotid gland showing a translocation (3;8)(p21;q12) and a deletion (5)(q22) as sole chromosome abnormalities

The cytogenetic findings in a mucoepidermoid tumor of the parotid gland are described. In addition to a t(3;8)(p21;q12), all cells analyzed showed a deletion of part of the long arm of chromosome 5. Although the typical translocation of benign pleomorphic adenomas was found, histologic examination did not show remnants of a pleomorphic adenoma. Nevertheless, we assumed that the malignant tumor most likely arose in a preexisting pleomorphic adenoma. As a mechanism for malignant transformation, the loss of a suppressor gene located on the long arm of chromosome 5 is discussed.