Cytogenetic study of a papillary thyroid carcinoma with a rearranged chromosome 10

Evidence for a 3p25 breakpoint hot spot region in thyroid tumors of follicular origin

Epithelial tumors of the thyroid are cytogenetically well-investigated tumors. So far, the main cytogenetic subgroups, characterized by trisomy 7 and by rearrangements of either 19q13 or 2p21, respectively, have been described. Recently, we have been able to describe the involvement of a novel gene called THADA in benign thyroid lesions with 2p21 rearrangements. Other fusion genes found in thyroid lesions are RET/PTC and PAX8/PPAR(gamma). The latter occurs in follicular thyroid carcinomas with a t(2;3)(q13;p25). Here we present molecular-cytogenetic and cytogenetic investigations on a follicular thyroid adenoma with a t(2;20;3)(p21;q11.2; p25). In this case, an intronic sequence of PPAR(gamma) is fused to exon 28 of THADA. We used BAC clones containing the genomic sequence of PPARgamma for fluorescence in situ hybridization to confirm the localization of the breakpoint within intron 2 of PPAR(gamma) . Our findings suggest that the close surrounding of PPAR(gamma) is a breakpoint hot spot region, leading to recurrent alterations of this gene in thyroid tumors of follicular origin including carcinomas as well as adenomas with or without involvement of PAX8.

Molecular cytogenetic characterization of chromosome 9-derived material in a human thyroid cancer cell line

The incidence of papillary thyroid carcinoma (PTC) increases significantly after exposure of the head and neck region to ionizing radiation, yet we know neither the steps involved in malignant transformation of thyroid epithelium nor the specific carcinogenic mode of action of radiation. Such increased tumor frequency became most evident in children after the 1986 nuclear accident in Chernobyl, Ukraine. In the eight years following the accident, the average incidence of childhood PTCs (chPTC) increased 70-fold in Belarus, 200-fold in Gomel, 10-fold in the Ukraine and 50-fold in Tschnigov, Kiev, Rovno, Shitomyr and Tscherkassy compared to the rate of about 1 tumor incidence per 106 children per year prior to 1986 (Likhtarev et al., 1995; Sobolev et al., 1997; Jacob et al., 1998). To study the etiology of radiation-induced thyroid cancer, we formed an international consortium to investigate chromosomal changes and altered gene expression in cases of post-Chernobyl chPTC. Our approach is based on karyotyping of primary cultures established from chPTC specimens, establishment of cell lines and studies of genotype-phenotype relationships through high resolution chromosome analysis, DNA/cDNA micro-array studies, and mouse xenografts that test for tumorigenicity. Here, we report the application of fluorescence in situ hybridization (FISH)-based techniques for the molecular cytogenetic characterization of a highly tumorigenic chPTC cell line, S48TK, and its subclones. Using chromosome 9 rearrangements as an example, we describe a new approach termed 'BAC-FISH' to rapidly delineate chromosomal breakpoints, an important step towards a better understanding of the formation of translocations and their functional consequences.

Anaplastic thyroid cancer: cytogenetic patterns by comparative genomic hybridization

We studied chromosomal abnormalities by comparative genomic hybridization (CGH) and flow cytometry in anaplastic thyroid cancer (ATC), and when present in coexisting or previous differentiated thyroid cancer (DTC). Overall 10 frozen tissues from patients with ATC and 5 cell lines (1 ATC and 4 DTCs) were analyzed. We found chromosomal abnormalities in 5 of 10 ATC tissues, with 24 abnormalities (22 gains and 2 losses). Among 8 ATCs that were associated with prior or concurrent DTC, more chromosomal abnormalities were found in ATC associated with follicular thyroid cancer (FTC) than those associated with PTC (median numbers 9.5 and 0.5, respectively, p = 0.046) or no associated differentiated thyroid cancer. Gain of 1q was relatively common in ATCs (30%). By flow cytometry, we found aneuploidy in 6 of 10 ATC tissues and diploidy in 4. There was concordance between DNA aneuploidy and the presence of chromosomal abnormalities by CGH in 4 of the 5 ATCs (p = 0.048). We also found 26 chromosomal abnormalities in an ATC cell line, 14.3 in 3 FTC cell line, and 3 in a PTC cell line. In conclusion, chromosomal abnormalities are frequent in ATCs associated with FTC, but uncommon in those associated with PTC and in ATCs with no associated differentiated thyroid cancer. These findings support the concept that PTC and FTC have different genetic backgrounds and, even after the transformation to ATC, they may retain some of their cytogenetic characteristics.

Controversies in papillary microcarcinoma of the thyroid

Papillary thyroid carcinomas that are smaller than 1 cm are classified as papillary microcarcinomas (PMC). These lesions are frequently detected as incidental findings on autopsy or in surgical specimens. They are often multifocal. The relationship between PMC and clinical papillary thyroid carcinoma (PTC) is not clear. In patients with clinical thyroid cancer, PMC may represent intrathyroidal metastases; they may be the earliest form of future large lesions. These uncertainties raise questions about appropriate clinical management of patients with these lesions. Review of the literature substantiates the argument that clinically evident PTC may be distinctly different from solitary or multifocal PMC in terms of etiology and biologic behavior, supporting a conservative approach to management.

Karyotypic characterization of papillary thyroid carcinomas

BACKGROUND

Cytogenetic studies performed in papillary thyroid carcinoma (PTC) identified chromosome 10q rearrangements with breakpoints at 10q11.2 as the most frequent aberrations in these tumors. In the current study, the authors aimed to identify other chromosomal abnormalities nonrandomly associated with papillary thyroid carcinomas.

METHODS

Cytogenetic analysis was performed on 94 papillary thyroid carcinomas after short-term culture of the tumors sterile fragments.

RESULTS

Clonal chromosomal changes were found in 37 tumors (40%). Structural cytogenetic abnormalities were observed in 18 carcinomas. Chromosomes 1, 3, 7, and 10 were the most frequently involved in rearrangements. Pooled results of the breakpoints detected in these tumors, as well as those described in the literature, allowed the authors to verify as the most common breakpoint loci 1p32-36, 1p11-13, 1q, 3p25-26, 7q34-36, and 10q11.2. The correlation between the karyotype features of the 94 PTCs and the histologic data revealed that some PTC follicular variants were characterized by chromosomal aberrations commonly found in thyroid follicular adenomas: a del(11)(q13q13), a t(2;3)(q13;p35), and gains of chromosomes 3, 5, 7, 9, 12, 14, 17, and 20. In the tall cell PTC variant group, 4 of the 7 tumors presented clonal cytogenetic changes, 3 (75%) of which were characterized by anomalies of chromosome 2 that lead to a overrepresentation of the long arm of this chromosome. Noted also in these series was an association between complex karyotypes and tumors with poorly differentiated histiotypes.

CONCLUSIONS

In this study, the authors report chromosome 1p32-36, 1p11-13, 3p25-26, and 7q32-36 as novel breakpoint cluster regions in PTC, and they suggest that there are cytogenetic changes preferentially associated with the follicular and tall cell PTC variants.

Translocations (X;10)(p22;q24) and (1;10)(q21;q11) in a follicular adenoma of the thyroid without apparent involvement of the RET protooncogene

We report here the cytogenetic analysis of a follicular adenoma of the thyroid which revealed an abnormal clone with a t(X;10)(p22;q24) and a t(1;10)(q21;q11) together with normal cells. Fluorescence in situ hybridization (FISH) with YACs 273E3 and 344H4, which are located on 10q11.2 and are specific for the RET protooncogene, showed no abnormalities. It would therefore appear that this gene is not involved in the particular tumor, as has been reported in a number of papillary thyroid carcinomas. Several chromosomal aberrations have been suggested as been specific for follicular thyroid adenoma. However, until now, only a few such cases have been reported which involve structural abnormalities of chromosomes 10q11.2 and 10q24. We believe this to be the first report of a follicular thyroid adenoma with a t(X;10)and a t(1;10).

DNA copy number changes in thyroid carcinoma

The genetic changes leading to thyroid cancer are poorly characterized. We studied DNA copy number changes by comparative genomic hybridization (CGH) in 69 primary thyroid carcinomas. In papillary carcinoma, DNA copy number changes were rare (3 of 26, 12%). The changes were all gains, and they were associated with old age (P = 0.01) and the presence of cervical lymph node metastases at presentation (P = 0.08). DNA copy number changes were much more frequent in follicular carcinoma (16 of 20, 80%) than in papillary carcinoma (P < 0.0001), and follicular carcinomas had more often deletions (13/20 versus 0/26, P < 0.0001). Loss of chromosome 22 was common in follicular carcinoma (n = 7, 35%), it was more often seen in widely invasive than in minimally invasive follicular carcinoma (54% versus 0%, P = 0.04), and it was associated with old age at presentation (P = 0.01). In three of the four patients with follicular carcinoma who died of cancer, the tumor had loss of chromosome 22. DNA copy number changes were found in 5 (50%) of the 10 medullary carcinomas studied. Four of these five carcinomas had deletions, and in two of them there was deletion of chromosome 22. Eleven (85%) of the thirteen anaplastic carcinomas investigated had DNA copy number changes, of which five had deletions, and one had deletion of chromosome 22. The most common gains in anaplastic carcinoma were in chromosomes 7p (p22-pter, 31%), 8q (q22-qter, 23%), and 9q (q34-qter, 23%). We conclude that DNA copy number changes are frequent in follicular, medullary, and anaplastic thyroid carcinoma but rare in papillary carcinoma when studied by CGH. Loss of chromosome 22 is particularly common in follicular carcinoma, and it is associated with the widely invasive type.

Double minutes in the papillary thyroid cancer cell line PTC-1113A

The cell line PTC-1113A was established from a metastasizing recurrent papillary thyroid cancer. The cell line was growing as monolayer and showed a complex karyotype with chromosome numbers ranging from 30 to 140/metaphase. A proportion of metaphases contained double minutes and/or pulverized chromosomes. Extrachromosomal DNA seemed to originate from a B-group chromosome. A chromosome 4 painting probe hybridized to extrachromosomal material, representing double minutes (dmin) and possibly minutes. In addition, fluorescence in situ hybridization (FISH) with the chromosome 4 library detected a translocation chromosome and a pulverized chromosome originating from chromosome 4. PTC-1113A is, to our knowledge, the single papillary thyroid cancer cell line demonstrating evidence of gene amplification.

Proto-RET is rearranged in the new human papillary thyroid cancer cell line PTC-1113A

The receptor tyrosine kinase proto-RET is believed to contribute to thyroid oncogenesis by activation of its tyrosine kinase either by point mutation or rearrangement. The papillary thyroid cancer cell lines PTC-1113A, L, and R were established from a recurrent thyroid cancer and its metastases. The rearrangement of the proto-ret oncogene in the cell line PTC-1113A is demonstrated by Southern analysis utilizing the probe for rearranged ret that encodes the fusion protein H4/tyrosine kinase. In contrast, rearranged ret alleles were not found in the cell lines that developed from metastases, nor in DNA isolated from the recurrent tumor. The cell line PTC-1113A may represent a population of tumor cells that gained a growth advantage due to rearranged ret. This is the second human thyroid cancer cell line harboring rearranged ret, and may serve to study the function of ret activation in thyroid cancers.

Cytogenetic findings in 31 papillary thyroid carcinomas

Chromosome studies performed on 31 papillary thyroid carcinomas (PTCs) revealed clonal numerical and structural abnormalities in 12 tumors. The numerical clonal aberrations found were trisomy 2, trisomy 7, and loss of the Y chromosome. A nonrandom telomeric association, tas(15;16)(p13;p13), was observed in one carcinoma. Structural alterations with a breakpoint at 10q11.2 were detected in two tumors. Other chromosomes involved in rearrangements were chromosomes 1, 2, 3, 5, 7, 9, 11, 12, and 14. The observation of clonal changes of chromosome 2 [i(2)(q10) and trisomy 2] in two tumors, which were both histologically classified as tall-cell PTC variants, suggests that gain of 2q may be important in the development of this morphological variant.

Recent advances in cytometry, cytogenetics and molecular genetics of thyroid tumours and tumour-like lesions

In this review we summarize the most recent advances of flow and image cytometry, cytogenetics and molecular genetics of tumours and tumour-like lesions of the thyroid, especially focusing on the putative relationship between nodular goitres and adenomas, the differential diagnosis of benign and malignant neoplasms and the pathogenesis and prognosis of carcinomas. Data obtained by in situ hybridization and immunohistochemical detection of proliferative markers, metal binding proteins and oncogenes, anti-oncogenes, growth factors and growth factor receptors are also used whenever appropriate.

Chromosomal aberrations in two adrenocortical tumors, one with a rearrangement at 11p15

Adrenocortical tumors are detected with increasing frequency, but symptomatic cases with excessive hormone production are rare. We investigated cytogenetically one benign aldosterone-producing tumor (Conn Syndrome)(case 1) and one malignant cortisol-producing tumor (Cushing Syndrome)(case 2). Radioimmunoassay of cell culture supernatant of case 2 detected cortisol secretion during 2 months in culture. Flow cytometry of spill-out cells from case 2 showed a bimodal pattern (DNA Index 1.0, 1.4). Case 1 revealed a marker chromosome in 4/25 cells analyzed; the marker was a long acrocentric partially derived from chromosome 2,der(2q). In case 2, a cytogenetic harvest was achieved after prolonged culture time (6 weeks) and a marker chromosome, add(11)(p15), was detected in 16/22 cells. A breakpoint of 11p13, as well as loss of heterozygosity of alleles on 11p15, has been reported in the literature for other malignant adrenocortical cancers.

Thyroid nodular hyperplasia: chromosomal studies in 14 cases

Cytogenetic study of 14 thyroid nodular hyperplasias revealed a hyperdiploid karyotype in two cases (14%) and a normal chromosomal complement in the remaining cases. Some of the numerical alterations found were identical to the ones considered characteristic of a subset of thyroid adenomas (+5, +7, +9, +12, +14, and +16). Our findings suggest that the cytogenetic events involved in the pathogenesis of thyroid hyperplastic lesions and benign tumors may be closely related, which supports the hypothesis of a biologic "continuum" between these two types of lesions.

Cytogenetic studies on 19 papillary thyroid carcinomas

Short-term cultures from 19 papillary thyroid adenocarcinomas revealed clonal numerical and/or structural chromosomal changes in 13 tumors, nonclonal abnormalities in one tumor, and only normal karyotypes in five tumors. Clonal abnormalities of chromosome 10 were present in three tumors, two of which had the translocation t(7;10)(q35;q21). Numerical abnormalities of chromosome 17 were detected in two tumors.

Cytogenetic and molecular genetic characterization of papillary thyroid carcinomas

A combined cytogenetic and molecular analysis was performed on 11 cases of papillary thyroid carcinoma. A simple karyotypic abnormality was detected in five tumors, whereas six had no apparent chromosome change. In four of five rearranged cases the presence of a specific chromosomal abnormality involving chromosome 10 (cases 1 and 2) and chromosome 1 (cases 3 and 4) was associated with the rearrangement of two protooncogenes: RET and NTRKI (formerly trk), respectively, with different donor genes. Moreover, the chromosomal localization of the involved genes and the type of chromosomal change observed suggested that RET and NTRKI activation occurred by intrachromosomal rearrangements. The six cases with normal karyotype did not show RET or NTRKI activation. These findings suggest that a combined cytogenetic and molecular approach would be useful in understanding the pathogenesis of thyroid neoplasia.

Significance of trisomy 7 in thyroid tumors

Standard cytogenetic studies of a multifocal metastasizing papillary thyroid carcinoma revealed two clonal chromosome aberrations: rearranged 10q and trisomy 7. Trisomy 7 seemed to be restricted to tumor nodule A, whereas era (10q) was detected in tumor nodule B and in a metastatic lymph node. We applied fluorescent in situ hybridization to ask whether trisomy 7 was a feature of the original tumor nodule or an in vitro phenomenon changing quantitatively during early passages and to see whether trisomy 7 was restricted to tumor nodule A. We used the biotinylated chromosome 7 alpha-satellite probe D7Z1 on freshly dropped slides from metaphase harvests from tumor nodule A,B, and the lymph node and on touch preparations from the frozen specimen of tumor nodule A. Trisomy 7 was present in the original tumor nodule (6% of cells), as well as in early passages (P1-3) from both tumor nodules and the metastatic lymph node with a frequency of 10.7-13.2%. The detection of trisomy 7 as a stable component in short-term cell culture and its presence in the original tumor material indicates that this common numerical aberration is an in vivo phenomenon.