Cytogenetics of the human benign mixed salivary gland tumour

Chromosome Translocations, Gene Fusions, and Their Molecular Consequences in Pleomorphic Salivary Gland Adenomas

Salivary gland tumors are a heterogeneous group of tumors originating from the major and minor salivary glands. The pleomorphic adenoma (PA), which is the most common subtype, is a benign lesion showing a remarkable morphologic diversity and that, upon recurrence or malignant transformation, can cause significant clinical problems. Cytogenetic studies of >500 PAs have revealed a complex and recurrent pattern of chromosome rearrangements. In this review, we discuss the specificity and frequency of these rearrangements and their molecular/clinical consequences. The genomic hallmark of PA is translocations with breakpoints in 8q12 and 12q13-15 resulting in gene fusions involving the transcription factor genes PLAG1 and HMGA2. Until recently, the association between these two oncogenic drivers was obscure. Studies of the Silver−Russel syndrome, a growth retardation condition infrequently caused by mutations in IGF2/HMGA2/PLAG1, have provided new clues to the understanding of the molecular pathogenesis of PA. These studies have demonstrated that HMGA2 is an upstream regulator of PLAG1 and that HMGA2 regulates the expression of IGF2 via PLAG1. This provides a novel explanation for the 8q12/12q13-15 aberrations in PA and identifies IGF2 as a major oncogenic driver and therapeutic target in PA. These studies have important diagnostic and therapeutic implications for patients with PA.

Activation of PLAG1 and HMGA2 by gene fusions involving the transcriptional regulator gene NFIB

The pleomorphic adenoma (PA), which is the most common salivary gland neoplasm, is a benign tumor characterized by recurrent chromosome rearrangements involving 8q12 and 12q14-15. We have previously shown that the PLAG1 and HMGA2 oncogenes are the targets of these rearrangements. Here, we have identified previously unrecognized subsets of PAs with ins(9;8)/t(8;9) (n = 5) and ins(9;12)/t(9;12) (n = 8) and breakpoints located in the vicinity of the PLAG1 and HMGA2 loci. RNA-sequencing and reverse transcriptase (RT)-PCR analyses of a case with an ins(9;8) revealed a novel NFIB-PLAG1 fusion in which NFIB exon 4 is linked to PLAG1 exon 3. In contrast to the developmentally regulated PLAG1 gene, NFIB was highly expressed in normal salivary gland, indicating that PLAG1 in this case, as in other variant fusions, is activated by promoter swapping. RT-PCR analysis of three PAs with t(9;12) revealed two tumors with chimeric transcripts consisting of HMGA2 exon 4 linked to NFIB exons 9 or 3 and one case with a fusion linking HMGA2 exon 3 to NFIB exon 9. The NFIB fusion events resulted in potent activation of PLAG1 and HMGA2. Analysis of the chromatin landscape surrounding NFIB revealed several super-enhancers in the 5'- and 3'-parts of the NFIB locus and its flanking sequences. These findings indicate that PLAG1 and HMGA2, similar to MYB in adenoid cystic carcinoma, may be activated by enhancer-hijacking events, in which super-enhancers in NFIB are translocated upstream of PLAG1 or downstream of HMGA2. Our results further emphasize the role of NFIB as a fusion partner to multiple oncogenes in histopathologically different types of salivary gland tumors.

Molecular cytogenetic pilot study on pleomorphic adenomas of salivary glands

Pleomorphic adenomas (PAs) of salivary glands are the most frequent entity of solid parotid tumors. Nonetheless, their genetics is not yet well understood. Thus, the current study characterized 14 PAs using a unique combination of cytogenetic, molecular cytogenetic and/or molecular karyotyping based approaches. The current study applied G-banding based on trypsin treatment and Giemsa-staining in peripheral blood and tumor tissue. Additionally, fluorescence in situ hybridization was performed using whole chromosome painting or centromeric probes. Array-based comparative genomic hybridization was also conducted. In 5 of 14 cases, chromosomal and/or submicroscopic alterations were characterized. Balanced and unbalanced translocations, loss or gain of whole chromosomes and submicroscopic copy number alterations were detected. Furthermore, the first case of a so-called ‘jumping translocation’ in a PA was reported. The genes twist-related protein 1 and distal-less homeobox 5 were also involved in copy number variations in two PAs. In conclusion, approaches utilized in the current study are highly suited to characterize the genetic constitution of PAs.

Case of extra pulmonary, pleuro-pulmonary blastoma in a child: pathological and cytogenetic findings

We report the cytogenetic findings in a case of Pleuro-Pulmonary Blastoma of Childhood Type II. This is a rare intrathoracic tumour that can occur in the lungs with up to 25% of cases being extra pulmonary.

Non-random chromosome rearrangements in adenoid cystic carcinoma of the salivary glands

The chromosomal findings in 10 adenoid cystic carcinomas (ACC) of the salivary glands are described. Clonal numerical deviations as the sole anomaly were detected in four cases and structurally rearranged stemlines and sidelines in four cases. An apparently identical t(6;9)(q23;p21) was found in two tumors; in one case the translocation was part of the abnormal stemline and in the other case it was the sole anomaly in a single variant cell. A similar or identical t(6;9)(q21-24;p13-23) has recently been reported in three of 15 previously published cases of ACC. The three remaining tumors with abnormal stemlines all had rearrangements of chromosome 9, including t(1;9)(q21;p21-22), der(9)i(9)(q10)inv(9)(q12q13), and der(X)t(X;9)(p21;p22-23), respectively. The latter case also had a t(17;18)(p12;q11.2) that was common to both abnormal clones present in this tumor. In addition to other abnormalities, the clone with der(X)t(X;9) also showed a del(6)(q13q21). In two cases fluorescence in situ hybridization (FISH) was used for further characterization of the marker chromosomes. A survey of the present findings together with previous results from 15 ACC clearly demonstrates that rearrangements of 6q21-24 (deletions or translocations in 11 cases), 9p13-23 (translocations in seven cases), and 17p12-13 (translocations in three cases) are recurrent, and often primary, in ACC, and that the t(6;9)(q21-24;p13-23), found in five tumors, is a non-random, primary aberration.

Cytogenetic abnormalities in an ossifying fibroma from a patient with bilateral retinoblastoma

Cytogenetic analysis of a cemento-ossifying fibroma from a patient with nonfamilial bilateral multicentric retinoblastoma revealed three reciprocal translocations with the karyotype 46,XY,t(1;18)(q21;q21.3),t(3;10)(p13;q22),t(6;11)(p22;p15). Routine and high-resolution cytogenetic analysis of peripheral blood leukocytes showed an apparently normal, 46,XY chromosome pattern with no deletion of chromosome 13. Molecular analysis demonstrated no gross differences in the retinoblastoma gene or the TP53 gene between constitutional and tumor DNA. This is the first cytogenetic analysis of a cemento-ossifying fibroma and the first report of this tumor in a retinoblastoma patient. The data may be added to the small, but growing literature on cytogenetic aberrations in benign tumors and may lend insight into genes involved in cell proliferation and neoplastic transformation.

Cytogenetic analysis of two sacral chordomas

Cytogenetic analysis of two sacral chordomas revealed two distinct abnormal clones in one of the cases: 44,XY,t(1;3)(q42;q11), -2,der(7)t(2;7)(q23;q32), -21 and 46,X,t(Y;8)(q12;q22), t(1;14)(p34;q32),t(5;10)(q13;p11). All cells analyzed from the second case were cytogenetically normal. To the best of our knowledge, chordomas have not previously been subjected to cytogenetic analysis.

Clear cell sarcoma with t(12;22) (q13-14;q12)

Karyotypic analysis of a clear cell sarcoma revealed a translocation t(12;22) (q13-14;q12) as a primary chromosomal change. This case is the third clear cell sarcoma cytogenetically analyzed; the two previously reported cases had t(12;22)(p11;p11), and a complex karyotype with trisomy 22, respectively.

Trisomy 8 as the only chromosome change in an epithelioid smooth muscle tumor

Epithelioid smooth muscle tumor is a rare low grade malignancy that usually occurs in the gastrointestinal tract. No chromosome studies of this tumor have been reported so far. We found trisomy 8 as the sole chromosome anomaly in a large hepatic epithelioid smooth muscle tumor.

Trisomy 8 as a nonrandom secondary change in myxoid liposarcoma

We report the cytogenetic findings in 5 cases of myxoid liposarcoma following short-term culture. In all 5 tumors a t(12:16)(q13:p11), characteristic of the myxoid form of liposarcoma, was observed. Trisomy 8 was present in two tumors as the only additional change and in a third in addition to other abnormalities. In the other two tumors the t(12:16) was present as the sole change. Three other myxoid liposarcomas with trisomy 8 as an additional aberration have been reported, suggesting that it could represent a non-random secondary event in these tumors.

Cytogenetic and molecular observations in human and experimental salivary gland tumors

The chromosomal banding patterns in 189 benign and malignant salivary gland tumors are reviewed. For comparison, karyotypic data from a recent series of polyoma virus-induced salivary gland tumors in the mouse are discussed. Special interest is focused on the relationships between the highly specific patterns of translocations and deletions in these tumors and different genes involved in neoplasia, in particular oncogenes, and tumor suppressor genes.

Clonal chromosome abnormalities with preferential involvement of chromosome 3 in patients with porokeratosis of Mibelli

Clonal chromosome abnormalities were found in cultured fibroblasts from three sibs and one sporadic case with porokeratosis of Mibelli. Chromosome 3 especially involved region p12-14. This region includes the most common fragile site in humans, and the proximal region of chromosome 3 short arm is involved in a variety of neoplastic conditions. We conclude that porokeratosis of Mibelli, an autosomal dominant disorder, is associated with chromosomal instability. Porokeratosis of Mibelli is known to also be associated with increased susceptibility to malignant disease. The chromosome instability may well predispose to malignancy.

Translocation (7;21) in a lipoma

Cytogenetic analysis was performed on a solitary lipoma from the flank of a 38-year-old male. A translocation t(7;21)(p22;q11.2) was found as the sole clonal chromosomal abnormality. The results are discussed in relation to other cytogenetic abnormalities found in benign adipose tumors.

Chromosomal composition of a series of 22 human low-grade gliomas

G-banded chromosomal analysis was performed on direct and/or in vitro cultures of 22 low-grade gliomas, including nine grade I-II astrocytomas, nine oligodendrogliomas, one mixed tumor oligodendroglioma-astrocytoma, and three ependymomas. Normal diploid stem lines were present in most astrocytomas and oligodendrogliomas, whereas, all three ependymomas displayed polyploid modal numbers. However, secondary cell lines showed the presence of clonal recurrent numerical abnormalities, mainly polysomy 7, monosomy 10 and 22, and loss of the Y chromosome. Clonal structural rearrangements were present with a low incidence; they mainly involved chromosomes #1 and #7. These patterns of chromosome involvement seem to correlate with the scarce previous cytogenetic banding data available from low-grade gliomas. They are also similar to the chromosome alterations found in high-grade gliomas.

Structural rearrangements of chromosome Nr 8 involving 8q12--a primary event in pleomorphic ademona of the parotid gland

Nine pleomorphic adenomas of the human parotid gland were investigated. Within this series the group of cases having clonal aberrations of chromosome Nr 8 predominates. The occurrence of cases with trisomy-8 and cases with structural rearrangements involving a breakpoint in 8q11-8q13 allows a further subdivision of this group of tumors. Our special interest in this paper is devoted to the latter group. The hypothesis is proposed that in these cases the chromosomal rearrangement is the primary event in tumorigenesis, leading to activation of a so far unknown oncogene located most likely at 8q12. The translocations to different recipient chromosomes may serve as sign posts to transcriptionally active chromosomal domains in the salivary gland.

Progression in a chemically induced transplantable human pancreas carcinoma

A methylnitrosourea (MNU)-induced transplantable human pancreas carcinoma was examined, at 3, 12, 18 and 36 months after its development, for growth and invasiveness in nude mice, karyotypic alteration and the evolution of marker chromosomes. Progression in tumorigenicity and invasiveness of cells were evident by a significant increase in tumor diameters produced within 8 weeks by the cells at 36 months as compared to those developed by cells from 3-month-old cell lines. Chromosome analysis at 3 months showed normal 46 XX karyotype in about 80% and minor anomalies in 20% of the cells. At 12, 18 and 36 months, all cells were hyperdiploid with 53-61 chromosomes and several abnormal marker chromosomes. Marker chromosomes showed non-reciprocal translocations, deletions, inversion and isochromosomes. The absence of chromosome 13 from the earlier stage onward may have resulted in the loss of genes which suppress tumorigenicity. The increase in homogeneously staining regions of marker chromosome 3 at later stages appears to parallel the augmentation in tumor growth and mitotic indices.

Recurrent deletions of chromosomes 11q and 3p in anal canal carcinoma

A cytogenetic study of 8 cases of anal canal cancer, including 1 cloacogenic and 7 squamous-cell carcinomas, was performed. All tumors exhibited chromosomal abnormalities. A rearrangement involving the long arm of chromosome 11 was seen in all instances, and, with the exception of the i (11q) found in one tumor, all the observed rearrangements resulted in a deletion of the distal segment. Rearrangements of chromosome 3, detected in 6 tumors, led to a deletion of the short arm in 5 cases. The association of these 2 deletions may characterize the anal canal carcinoma, the smallest common deleted segments being distal to 11q22 or q23 and 3p22.

Cytogenetic studies of human brain tumors and their clinical significance. II. Meningioma

Cytogenetic study of 45 meningiomas from 31 female and 14 male patients are reported. No chromosomal abnormalities were found in nine (20%). These were predominantly meningotheliomatous, and were from younger patients (average age, 46 years). Monosomy 22 was noted in only 20% and in 12 patients (27%) with other losses and rearrangements. Among the latter, 50% were either recurrent or recurrent and invasive, the majority were fibromatous and occurred in older patients. Nonrandom loss was observed of the Y and abnormalities of chromosomes #1, #7, and #14 and, to a lesser extent, chromosomes #18, #19, and #20. Meningiomas may begin with no chromosomal abnormalities, having meningotheliomatous histopathologic appearance, occur in younger patients, and are less aggressive. Karyotypic evolution following loss of a chromosome #22 continues with losses and rearrangements of other chromosomes with apparent nonrandom involvement of chromosomes #1, #7, #14 and Y. This karyotypic change is associated with aggressive tumor behavior and fibromatous morphology.

Cytogenetic clones in a recurrent neurofibroma

Chromosome studies were performed on a plexiform neurofibroma arising in a probable von Recklinghausen's disease patient, who also showed a de novo constitutional reciprocal translocation, t(1;22)(p32;q11). Banding analysis of the metaphases obtained from two primary cultures in vitro showed the presence of five cytogenetic clones, characterized by different chromosomal rearrangements. In addition to t(1;22), marker chromosomes involved pairs 1, 2, 3, 5, 8, 9, 10, 12, 16, and X. These findings suggest a possible polyclonal evolution in this neurofibroma.

Aberrations of chromosome 8 in mixed salivary gland tumors--cytogenetic findings on seven cases

Cytogenetic findings on seven mixed salivary gland tumors are reported herein. The involvement of chromosome #8 in clonal chromosome aberrations in five of the seven tumors was particularly noteworthy. Four tumors had translocations involving chromosome #8 and one or two other chromosomes (#3, #7, #9, #13). The fifth showed a deletion of parts of the long arm of chromosome #8. In an attempt to define the critical segment on chromosome #8, we have identified the part between 8q11 and 8q13 as the critical region involved in all rearrangements. Thus far, our results confirm the results of the Swedish group, though the percentage of cases having #8 abnormalities is somewhat higher in our small series. The relationship between the two groups of cases, those with and those without chromosome abnormalities, will be discussed.

The cytogenetics of solid tumors. Relation to diagnosis, classification and pathology

This overview discusses the chromosome changes in solid tumors and how recent advancements in techniques have yielded results which at least qualitatively are similar to those obtained in the leukemias, i.e., that consistent and recurrent chromosome changes characterize most tumors adequately examined and that tumor entities consist of cytogenetically defined and unique subsets. Thus, the findings point to a similar application of the chromosome changes in tumors in their classification, diagnosis and causation.

Cytogenetic studies of adipose tissue tumors. I. A benign lipoma with reciprocal translocation t(3;12)(q28;q14)

Detailed clinical histories and cytogenetic investigations using short-term cultures are reported in three typical benign lipomas. Although a diploid (normal) karyotype was observed in two cases, a reciprocal chromosome translocation t(3;12)(q28;q14) was found in the third case, which was briefly reported previously. These data are discussed in light of a lipoma with similar karyotypic changes reported by Heim et al. and a similar translocation observed by us in malignant myxoid liposarcomas. The nonrandom involvement of segment 12q13-q14 in benign and malignant lipomatous tumors suggest a common basis for at least one of the possible multiple steps in the genesis of neoplastic processes.

A case of pituitary adenoma with 58 chromosomes

Chromosome analysis was performed on a growth hormone secreting pituitary adenoma. G-banding analysis showed a stem line with 58 chromosomes including numerical deviations of pairs #3, #5, #7, #9, #11, #12, #13, #17, #19, #20, and gonosomes was found. These findings add new evidence of the nonrandom involvement of C and F group chromosomes in numerical deviations in this tumor type.

6q- and loss of the Y chromosome--two common deviations in malignant human salivary gland tumors

Nine cases of malignant human salivary gland tumors cultured in vitro were subjected to detailed cytogenetic analysis with G-banding. Together with observations from three earlier published cases, the results of 12 cases were surveyed: five adenoid cystic carcinomas, three acinic cell tumors, three adenocarcinomas, and one mucoepidermoid carcinoma. All tumors had stemlines in the diploid-near-diploid mode. The most consistent changes among the adenoid cystic carcinomas were stem lines and/or variant cells with anomalies affecting the terminal part of 6q (i.e., 6q 16-25). Deviations affecting the Y chromosome (losses) and, to a lesser extent, #6 (structural changes) and #8 (gains) characterized the early karyotypic evolution in acinic cell tumors. Two of the three analyzed adenocarcinomas showed stemlines or variant cells with loss of gonosomes. The karyotypic features of the different tumor types, including primary changes, evolutionary characteristics, and progressional pathways, are discussed. The cytogenetic relationships between benign and malignant salivary gland tumors also will be considered.

The most common fragile site in man is 3p14

In man a common fragile site is known to occur at 3p14. We studied the expression of this fragility in a group of 70 normal healthy subjects. Chromosome breaks, chromatid breaks and gaps at 3p14 could be observed in every examined individual, and in a total of 7000 metaphases they were seen in a mean of 4% of cells. Fluorescence studies in ten persons with chromosome No. 3 polymorphism showed that in all cases both Nos. 3 were about equally liable to breakage. A considerable variation in the fra 3p14 expression was found between individuals as well as in repeated cultures from the same person. Neither sex nor age influences could be detected. Cultures with a high percentage of lesions at 3p14 tended to have also a high number of lesions at other sites. Methotrexate and fluorodeoxyuridine markedly enhanced the expression of fra 3p14 and other fragilities. It is concluded that the chromosomal region at 3p14 represents man's most common fragile site, the expression of which seems to be influenced by environmental and heritable factors.

Observations by G-banding in benign odontogenic tumors

The G-banding patterns in five cultured benign odontogenic tumors are described. Abnormal stem sideline karyotypes were observed in two tumors, whereas the remaining three tumors had a normal stemline. The latter cases, however, contained different types of variant cells, often showing deviations of nonrandom character. The results are discussed in relation to chromosomal findings in other benign tumor types and, briefly, in relation to oncogenes. A stepwise evolutionary pattern, which might be common to all benign tumor types, is suggested.

Intermediate filaments in cultured human pleomorphic adenomas. An immunohistochemical study

Primary cultures of 9 benign human pleomorphic adenomas were analyzed by immunofluorescence and antibodies against the different intermediate filaments and microfilaments. The cultured cells were also cytogenetically characterized by G- and C-banding techniques. The adenoma cells expressed at least three different classes of intermediate filaments, viz. prekeratin, vimentin and glial fibrillary acidic protein (GFA). No correlation between chromosomal pattern and intermediate filament expression was found. The frequency of cells stained for each of the different antibodies varied considerably among the tumours. Prolonged culturing appeared to induce a reduction of cells positive for prekeratin. This was probably a true loss of antigens and not an effect of overgrowth of stromal cells. It is concluded that the cells studied, on the basis of several criteria, are of neoplastic origin. This in vitro system appears to be well suited for further histogenetic studies on pleomorphic adenomas.

Human ameloblastomas in vitro: light microscopical and ultrastructural observations

The light microscopical and ultrastructural morphology in vitro of one case each of human plexiform, follicular and acanthomatous ameloblastoma are described. Ultrastructural analysis of cultured tumour cells revealed that the main cell type growing in vitro displayed morphological features typical of columnar cells or preameloblast-like cells of ameloblastomas. Irrespective of histological type all cases showed indistinguishable in vitro light microscopical and ultrastructural morphology. These findings strongly suggest that the columnar cell type accounts for the main proliferative capacity of ameloblastomas in vitro and most likely also in vivo.

3'-Terminal region of avian carcinoma virus MH2 shares sequence elements with avian sarcoma viruses Y73 and SR-A

We determined the nucleotide sequence of the acute transforming avian retrovirus MH2 from an HgiAI site within the coding region of its oncogene, v-myc, to the KpnI site within the long terminal repeat. Comparison with published sequences from other retroviruses allowed us to identify all sequence elements in this region. We conclude that MH2 contains a unique assembly of 3'-terminal sequences, which includes part of the helper virus-derived SPC region of avian sarcoma virus Y73 and the complete F3 and F1 segments of Rous sarcoma virus strain SR-A.