Development Of Thyroid Tumors Research Articles

Ethane Sulfonate Metabolite of Alachlor: Assessment of Oncogenic Potential Based on Metabolic and Mechanistic Considerations

Chronic administration of alachlor has been shown to produce neoplastic responses in the nasal turbinate mucosa, glandular stomach mucosa, and thyroid follicular epithelium of rats. Subsequent studies have shown that specific metabolic activation of alachlor is required for nasal tumor formation, and that non-genotoxic, threshold-sensitive processes produce all three tumors. The herbicide alachlor is degraded in the soil by microbial action to the tertiary ethane sulfonate metabolite (ESA). The acute and subchronic toxicity of ESA is very low, and the metabolite did not produce developmental toxicity or genotoxicity. The studies described here were conducted to determine whether ESA shares a common mechanism of oncogenicity with alachlor in rats. Specifically, we studied ESA's pharmacokinetics and ability to produce changes that are causally associated with the oncogenicity of alachlor. These studies demonstrated that ESA was poorly absorbed and underwent minor metabolism, which contrasted with the significant absorption and substantial metabolism observed with alachlor. ESA was also excreted more quickly than alachlor and showed no evidence of accumulation in the nasal turbinates, a site of oncogenicity for alachlor in the rat. In addition, ESA did not elicit the characteristic preneoplastic changes observed in the development of alachlor-induced nasal, stomach, and thyroid tumors. The results of these studies support the conclusion that ESA does not share a common oncogenic mechanism with alachlor and would not be expected to produce the same oncogenic responses observed following chronic alachlor exposure in rats.

Absence of the c-Ha-ras and c-Ki-ras oncogene mutations in the hermaphroditic fish Rivulus marmoratus papillary thyroid carcinomas induced by N-methyl-N'-nitro-N-nitrosoguanidine

Previously we reported that papillary thyroid carcinomas were predominantly induced at high frequency by a low dose of N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) in the hermaphroditic fish Rivulus marmoratus. In the current study, polymerase chain reaction (PCR) amplification and direct sequencing were used to examine the point mutations of Ha- and Ki-ras genes, which may be associated with papillary thyroid tumour development in rivulus. Thirty-three tumour samples were tested, however, no mutations were detected in rivulus Ha- and Ki-ras genes. In human and rodent models, it has been reported that ras gene mutations in papillary thyroid tumours occurred preferentially in the N-ras gene in general, while follicular tumours contained activated Ha- or Ki-ras gene mutations. This may explain why papillary thyroid carcinomas in rivulus were not mutated at codon 12, 13 or 61 of exon 1 or exon 2 of the rivulus Ha- or Ki-ras gene. These results imply that another oncogene, such as the N-ras gene and others, may be preferentially activated in rivulus papillary thyroid carcinomas, and also give valuable information for comparative studies of papillary thyroid carcinogenesis.

P53 mutations in tumors derived from irradiated human thyroid epithelial cells

A non-tumorigenic human thyroid epithelial cell line (HTori-3) has been transformed into tumorigenic cells by exposure in vitro to alpha particles or gamma-radiation. These transformants were tumorigenic in athymic nude mice and tumors were transplantable into other nude mice. To further characterize processes involved in neoplastic progression, the tumor cell lines derived from these radiation-induced primary tumors were screened for mutations in the p53 tumor suppressor gene. p53 mutation was detected by single-strand conformation polymorphism (SSCP) analysis of exons 5 to 8 inclusive. Mutations detected by SSCP analysis were confirmed by sequencing. Mutations were detected in all four exons analysed, although there was no correlation between dose, LET or mutation position or frequency. Mutations in p53 exons 6 and 7 have been reported in the childhood papillary thyroid carcinomas in Belarus presumably as a result of radioiodine fall-out. Similarly here, p53 mutations are induced experimentally during the development of human thyroid tumors generated by irradiation of a human thyroid epithelial cell line in vitro.

Expression of c-erbB-2 oncoprotein in human thyroid tumours.

c-erbB-2 expression has been found to be a potential marker of aggressive biological behaviour in some tumours, but the role played by this oncoprotein in the development and maintenance of thyroid tumours is still controversial. Therefore our objective was to determine whether c-erbB-2 was overexpressed in a large retrospective series of human thyroid tumours, including both from follicular and C-cell differentiation. We have studied 67 thyroid tumours (10 follicular adenomas, 11 follicular carcinomas, three anaplastic carcinomas, 25 papillary carcinomas and 18 medullary carcinomas and 16 metastases) by immunohistochemistry using an antigen retrieval method for paraffin-embedded material and a specific polyclonal antibody against the intracytoplasmic part of c-erbB-2 oncoprotein. There are marked differences in the pattern of c-erbB-2 immunoreactivity depending on the type of thyroid tumour. Thus, no expression of the oncoprotein has been found in follicular adenomas, follicular carcinomas and anaplastic carcinomas, but 52% of papillary carcinomas (membranous and diffuse cytoplasmic patterns) and all medullary carcinomas (granular cytoplasmic pattern) are immunopositive. Our results indicate that overexpression of c-erbB-2 oncoprotein is easily identifiable by immunohistochemistry in paraffin sections of certain thyroid tumours after applying an antigen retrieval method. This study suggests that c-erbB-2 oncoprotein may play some role in disease progression in papillary and medullary thyroid carcinomas, but the significance of the different immunohistochemical patterns merits further investigations.

Impaired DNA Repair as Assessed by the “Comet” Assay in Patients with Thyroid Tumors After a History of Radiation Therapy: A Preliminary Study

Purpose: Patients with a history of head and neck irradiation in childhood are at risk to develop thyroid tumors. The aim of this study was to determine if an impairement of DNA strand breaks repair could account for this observation. Methods and Materials: Circulating unstimulated lymphocytes of a group of 13 patients who developed thyroid tumors after radiotherapy were submitted to the alkaline single-cell gel electrophoresis assay (SCGE or “comet” assay) after in vitro exposure to 2 and 5 Gy of γ-rays. A control group of 8 healthy donors and 2 cases with a history of neck irradiation who did not develop a thyroid tumor were also analysed. The immediate response was compared to that observed after 15, 30, and 60 min of postexposure incubation periods. Results: Induction of DNA strand breaks is a dose–dependent process. The SCGE assay parameters did not differ significantly between patients and controls immediately ( t = 0) after irradiation at the two doses used. As compared to healthy donors, a slower kinetics of repair was found in the patients. The proportion of residual damage at 60 min postirradiation was significantly ( p < 0.01) higher in patients than in controls, at both doses analysed. Flow cytometric analysis of apoptosis and p53 protein status studied before and after irradiation showed no apparent relationship with the repair capacity. Conclusion: This preliminary study suggests that a subgroup of patients who develop thyroid tumors after a history of irradiation are partially defective in the late restitution of in vitro radiation-induced DNA strand breaks. This deficiency could be a predisposing factor to radiation-associated thyroid tumorigenesis. Detection of susceptible individuals using the simple and rapid comet assay, especially children receiving radiotherapeutic treatment, may allow a preventive surveillance for radiation-associated epithelial thyroid tumor development.

The ret/ptc1 oncogene is activated in familial adenomatous polyposis-associated thyroid papillary carcinomas.

Familial adenomatous polyposis (FAP) is caused by germ-line mutations of the apc gene, and it is associated with an increased risk of developing papillary thyroid carcinomas. We have previously reported that a significant fraction of sporadic human papillary thyroid carcinomas is characterized by gene rearrangements affecting the ret protooncogene. These rearrangements generate chimeric transforming oncogenes designated ret/ptc. By a combined immunohistochemical and RT-PCR approach, we analyzed, for ret/ptc oncogene activation, papillary thyroid carcinomas occurred in two FAP kindreds, both showing typical apc gene mutations. Kindred 1 had seven members affected by FAP, and among these, three patients showed papillary thyroid carcinomas. Kindred 2 had two patients, mother and daughter, affected by colonic polyposis; the 20-yr-old daughter showed also a papillary carcinoma. Here we report that ret/ptc1 oncogene was activated in two of the three papillary carcinomas of FAP kindred 1 and in the papillary carcinoma of FAP kindred 2. These findings document that loss of function of apc coexists with gain of function of ret in some papillary thyroid carcinomas, suggesting that ret/ptc1 oncogene activation could be a progression step in the development of FAP-associated thyroid tumors.

Thyroid carcinomas in RET/PTC transgenic mice.

The RET/PTC oncogene, a rearranged form of the RET proto-oncogene, has been found to be associated with human papillary thyroid carcinomas. To investigate whether RET/PTC causes papillary thyroid carcinoma, we generated a transgenic mouse model of papillary thyroid carcinoma with targeted expression of RET/PTC1 in the thyroid gland. Thyroid tumors in these RET/PTC1 transgenic mice are characterized by a slow growth rate, thyroid-stimulating hormone (TSH)-responsive tumor progression, and loss of radioiodide-concentrating activity despite continued expression of thyroglobulin (Tg). The time of tumor onset appears to be dependent on the expression level of RET/PTC1 in these transgenic mice. In high-copy RET/PTC1 transgenic mice, cellular abnormalities, including a slightly increased proliferation rate, aberrant follicle formation, and loss of radioiodide-concentrating activity, can be readily identified at embryological day 18. To identify which signaling pathway or pathways perturbed by RET/PTC1 are essential for RET/PTC1 to induce tumor development, we generated transgenic mice carrying a thyroid-targeted RET/PTC1 triple mutant, which contains tyrosine to phenylalanine mutations at tyrosine residues 294, 404, and 451. Initial characterization of the thyroid glands of these RET/PTC1 triple-mutant transgenic mice showed no change in follicular morphology or radioiodide-concentrating activity. This finding suggests that signaling pathways mediated by one or more of these three phosphotyrosine binding sites are essential for RET/PTC1 to induce thyroid tumor development. Finally, in order to investigate whether tumors induced by RET/PTC3 are more aggressive than those tumors induced by RET/PTC1, we also generated thyroid-targeted RET/PTC3 transgenic mice.

Oncogenic rearrangements of the ret proto-oncogene in thyroid tumors induced after exposure to ionizing radiation

A high frequency (≃ 60%) of ret rearrangements in Chernobyl papillary thyroid c, reinomas (PTC) has been reported recently. The data suggested that the radiation exposure may be a direct inducer of activating rearrangements in the ret gene. In our study, we have analyzed for the presence of RET/PTC oncogenes using the RT-PCR, XL-PCR. Southern blot and direct sequencing techniques, 39 human thyroid tumors from patients who had received external radiation for benign or malignant conditions. As controls, we studied 39 ‘spontaneous’ tumors. Our results indicate that: 1) the overall frequency of ret rearrangements was 84% in papillary carcinomas ( 16 19 ) and 45% ( 9 20 ) in follicular adenomas; 2) in contrast with the results obtained in the Chernobyl tumors, the most frequently observed chimeric gene was RET/PTC1; and 3) all the tumors were negative for RET/PTC2. In the ‘spontaneous’ tumors, only the papillary carcinomas presented a ret rearrangement (15%; 3 20 ). Our data confirm the crucial role played by the ret proto-oncogene activating rearrangements in the development of radiation-associated thyroid tumors, and show, for the first time, the presence of RET/PTC genes in follicular adenomas appeared after external irradiation.

High prevalence of activating ret proto-oncogene rearrangements, in thyroid tumors from patients who had received external radiation.

A high frequency (about 60%) of ret rearrangements in papillary thyroid carcinomas of children exposed to radioactive fallout in Belarus after the Chernobyl accident, has been reported by three recent studies (Fugazzola et al., 1995; Ito et al., 1994; Klugbauer et al., 1995). These studies suggested that the radiation exposure may be a direct inducer of activating rearrangements in the ret gene. In order to confirm the postulated link between irradiation and the role of the ret proto-oncogene in thyroid tumorigenesis, we analysed for the presence of ret activating rearrangements using RT-PCR, XL-PCR, Southern blot and direct sequencing techniques, 39 human thyroid tumors (19 papillary carcinomas and 20 follicular adenomas), from patients who had received external radiation for benign or malignant conditions. As controls, we studied 39 'spontaneous' tumors (20 papillary carcinomas and 19 follicular adenomas). Our data concerning the radiation-associated tumors, showed that: (1) the overall frequency of ret rearrangements was 84% in papillary carcinomas (16/19) and 45% (9/20) in follicular adenomas; (2) in contrast with the results obtained in the Chernobyl tumors, the most frequently observed chimeric gene was RET/PTC1 instead of the RET/PTC3 and (3) all the tumors were negative for RET/PTC2. In the 'spontaneous' tumors, only the papillary carcinomas presented a ret rearrangement (15%:3/20): 1 RET/PTC1, 1 RET/ PTC3 and 1 uncharacterized. In conclusion, our results confirm the crucial role played by the ret proto-oncogene activating rearrangements in the development of radiation-associated thyroid tumors appearing after therapeutic or accidental ionizing irradiation, and show, for the first time, the presence of RET/PTC genes in follicular adenomas appeared after external irradiation.

Mechanistic data and risk assessment of selected toxic end points of the thyroid gland.

Many goitrogenic xenobiotics that increase the incidence of thyroid tumors in rodents exert a direct effect on the thyroid gland to disrupt one of several possible steps in the biosynthesis, secretion, and metabolism of thyroid hormones. This includes (a) inhibition of the iodine trapping mechanism, (b) blockage of organic binding of iodine and coupling of iodothyronines to form thyroxine (T4) and triiodothyronine (T3), and (c) inhibition of thyroid hormone secretion by an effect on proteolysis of active hormone from the colloid. Another large group of goitrogenic chemicals disrupts thyroid hormone economy by increasing the peripheral metabolism of thyroid hormones through an induction of hepatic microsomal enzymes. This group includes central nervous system-acting drugs, calcium channel blockers, steroids, retinoids, chlorinated hydrocarbons, polyhalogenated biphenyls, and enzyme inducers. Thyroid hormone economy also can be disrupted by xenobiotics that inhibit the 5'-monodeiodinase that converts T4 in peripheral sites to biologically active T3. Inhibition of this enzyme by FD&C Red No. 3 lowers circulating T3 levels, which results in a compensatory increased secretion of thyroid-stimulating hormone (TSH), follicular cell hypertrophy and hyperplasia, and an increased incidence of follicular cell tumors in 2-yr or lifetime studies in rats. Physiologic perturbations alone, such as the feeding of an iodine-deficient diet, partial thyroidectomy, natural goitrogens in certain foods, and transplantation of TSH-secreting pituitary tumors in rodents also can disrupt thyroid hormone economy and, if sustained, increase the development of thyroid tumors in rats. A consistent finding with all of these goitrogens, be they either physiologic perturbations or xenobiotics, is the chronic hypersecretion of TSH, which places the rodent thyroid gland at greater risk to develop tumors through a secondary (indirect) mechanism of thyroid oncogenesis associated with hormonal imbalances.

Origin and progression of thyroid epithelial tumours: cellular and molecular mechanisms.

Tumours of the thyroid follicular cell are proving to be one of the most informative models for "dissecting' the molecular genetics of multi-stage human tumorigenesis. Early thyroid tumour development is closely correlated with mutation of five alternative genes, ras, ret, trk, gsp and the TSH receptor, associated with different tumour phenotypes, providing an excellent example of genotype/phenotype correlation. For two of these genes, ras and ret, there is also direct experimental evidence from gene transfer studies that they are sufficient to initiate tumorigenesis, one of very few situations where such proof of causality has been obtained for a human tumour. Much less is known of the molecular basis of malignant transformation in thyroid. However, the rare, further progression to undifferentiated (anaplastic) cancer provides a particularly clear-cut illustration of the role of the tumour-suppressor gene p53 in human cancer. Furthermore, in vitro data suggest the intriguing possibility that the anaplastic phenotype results from a combination of p53 mutation together with a spontaneous switch in differentiation programme, i.e. co-operation between a genetic and an epigenetic event.

Trisomy 18 in a canine thyroid adenoma

A canine thyroid adenoma showing trisomy 18 as the sole clonal cytogenetic abnormality (9 of 30 analyzed metaphases) is reported. Because trisomies are a recurrent cytogenetic finding in human benign thyroid tumors as well, it is suggested that the molecular relationship between these trisomies and the development of thyroid tumors can be determined by comparative gene mapping.

Status and expression of the p16INK4 gene in human thyroid tumors and thyroid‐tumor cell lines

The p16INK4 tumor-suppressor gene (also known as CDKN2, CDK41 and MTSI) encodes a negative regulator of the cell cycle. This gene, located in 9p21, is mutated or homozygously deleted in a high percentage of tumor cell lines and specific types of primary tumors. We have examined the status of the p16INK4 gene in 31 thyroid tumors and 7 thyroid cell lines. No DNA abnormalities were found in primary tumors. Conversely, p16INK4 gene structural alterations, deletions and point mutations were found in 4 thyroid cell lines. The expression of the 2 different p16INK4 mRNAs, the p16α and p16β transcripts, was determined by RNA-PCR experiments. All the primary thyroid tumors expressed the β transcript, while the p16α was barely detectable. The thyroid cell lines always expressed the p16β transcript, while the α transcript was absent or, whenever present, coded for a mutated form of the p16INK4 gene product. Taken together, our results suggest that loss of p16INK4 function is not directly involved in the process of thyroid-tumor development, but it probably gives cells in tissue culture a selective growth advantage. © 1996 Wiley-Liss, Inc.

Status and expression of thep16INK4 gene in human thyroid tumors and thyroid-tumor cell lines

The p16INK4 tumor-suppressor gene (also known as CDKN2, CDK41 and MTS1) encodes a negative regulator of the cell cycle. This gene, located in 9p21, is mutated or homozygously deleted in a high percentage of tumor cell lines and specific types of primary tumors. We have examined the status of the p16INK4 gene in 31 thyroid tumors and 7 thyroid cell lines. No DNA abnormalities were found in primary tumors. Conversely, p16INK4 gene structural alterations, deletions and point mutations were found in 4 thyroid cell lines. The expression of the 2 different p16INK4 mRNAs, the p16alpha and p16beta transcripts, was determined by RNA-PCR experiments. All the primary thyroid tumors expressed the beta transcript, while the p16alpha was barely detectable. The thyroid cell lines always expressed the p16beta transcript, while the alpha transcript was absent or, whenever present, coded for a mutated form of the p16INK4 gene product. Taken together, our results suggest that loss of p16INK4 function is not directly involved in the process of thyroid-tumor development, but it probably gives cells in tissue culture a selective growth advantage.

The aetiology, investigation and management of surgical disorders of the thyroid gland.

There have been many recent advances in our understanding of thyroid disease, including thyroid physiology, the molecular biology of thyroid neoplasms, guidelines for the management of surgical thyroid disease and the operative approach to thyroidectomy. The control of thyroid growth and function is better understood now that the thyroid stimulating hormone (TSH) receptor has been characterized as a G-protein coupled transmembrane receptor. The peripheral action of thyroid hormones is also better understood in terms of their interaction with nuclear thyroid hormone receptors. An adenoma-carcinoma sequence for the development of thyroid neoplasms has been proposed based on the characterization of a number of proto-oncogenes and tumour suppressor genes, and different pathways for the development of papillary and follicular thyroid carcinoma have been demonstrated. Fine needle biopsy has become, over the past few years, the principal diagnostic technique for evaluation of thyroid nodules, and has resulted in a significant reduction in the need for surgery for benign thyroid nodules. The approach to the management of thyroid carcinoma can now be based on comprehensive scoring systems for assigning patients to a particular risk group, the most recent of which is the MACIS system based on distant metastases (M), age (A), completeness of resection (C), invasion (I) and size (S). The capsular technique of thyroidectomy as described has now been shown to be the best method to preserve parathyroid blood supply, protect the recurrent laryngeal nerve and minimize the complications of thyroid surgery.

Mechanisms and pathogenesis of thyroid cancer in animals and man

The transformation of the normal fully differentiated thyroid follicular cell to the rapidly growing undifferentiated anaplastic thyroid carcinoma cell involves a number of stages which have been defined morphologically and are now being related to various growth pathways and to molecular biological defects. The two main factors involved in this transformation are growth stimulation and mutagenesis. Growth stimulation alone, through elevated TSH, can lead to the development of thyroid tumours, usually benign, and retaining TSH dependency in some cases. Mutagens alone, if growth is suppressed, do not produce tumours, the combination of mutagens and increased growth is a potent carcinogenic regime. Non-genotoxic carcinogenesis in the thyroid involves growth, without mutagenesis the agent often causes this through affecting one component of thyroid hormone synthesis or metabolism, leading to a fall in thyroid hormone levels and a rise in TSH. Growth stimulation increases the rate of cell division, and therefore increases the chance of a mutation. Continued growth increases the change of subsequent events, in particular loss of heterozygosity in a tumour suppressor gene. The main oncogenes involved in human thyroid carcinogens are ras in the follicular tumour pathway, and ret in the papillary carcinoma pathway. p53 is involved in the progression of either papillary or follicular adenoma to an undifferentiated carcinoma. In experimental thyroid carcinogenesis, ras is again involved, with a link between the mutagenic agent used and the type of ras gene showing mutation. Analysis of the involvement of different growth factors and oncogenes in thyroid carcinogenesis suggests that genes related to the two receptors concerned with normal TSH stimulated growth, TSH receptor and the IGF1 recpptor may be involved in the progression of thyroid tumours of follicular pathology. Several tyrosine kinase receptors with unknown ligands or of uncertain physiological function are linked to papillary carcinoma. The recent large increase in papillary carcinoma of the thyroid in children exposed to fallout from the Chernobyl nuclear accident underlines the importance of understanding the pathobiology of thyroid neoplasia.

Allelotyping of follicular thyroid tumors

To elucidate further the genetic mechanisms for follicular thyroid tumor development and progression, we allelotyped follicular thyroid tumors and other thyroid lesions from 92 patients. In general, a low frequency of loss of heterozygosity (LOH) was found, the highest being for chromosomes 3q, 10q, 11p, 11q, 13q, and 22q (10%-15%). However, detailed study of LOH of these chromosome arms with regard to the different histopathological diagnoses indicates that a locus on chromosome 10q may be involved in follicular thyroid tumor progression. In addition, the majority of Hürthle cell adenomas showed LOH on either chromosome 3q or 18q, in contrast to the other tumor types. This discrepancy in genetic alterations may contribute to the divergent clinical features occurring in these tumors.

FD&C Red No. 105 (Rose Bengal B) neutralizes the thyroid tumor promoting effect of iodine-deficient diet in rats

The effect of 3,4,5,6-tetrachloro-2′,4′,5′,7′-tetraiodo-fluorescein sodium salt (Rose Bengal B or FD&C Red No.105, molecular weight 1017.6) on the thyroid of rats treated with N-bis(2-hydroxypropyl)-nitrosamine (DHPN) and iodine-deficient (I-def) diet is studied. Six-week-old male F344 rats were divided into seven groups (20 each) and given a single subcutaneous injection of DHPN (2800 mg/kg body wt). From week 2 to 20, I-def diet was given in combination with either FR105 (1.25, 5.0, or 20 mg/1) or potassium iodide (KI, 12.5, 50.0 or 200 μg/1) in drinking water. As a result, an amount of 1.25 mg/1 of FR105 was slightly more effective than 200 μg/1 of KI in terms of inhibition of the effect of I-def diet on thyroid weight, morphology, thyroid-related hormones and thyroid tumor development. It was calculated that 1 μmol/1 of FR105 was slightly more potent than 1 μmol/1 of iodide ion. As each FR105 molecule has four iodide residues, at least 25% of total iodide residues were calculated to be utilized by the rats given I-def diet.

Oncogenic Activation of the ret Protooncogene in Thyroid Cancer

Recent studies have established that the ret protooncogene is involved in the development of thyroid tumors, including medullary and papillary thyroid carcinomas. Germ line mutations of the ret protooncogene were identified in multiple endocrine neoplasia (MEN) types 2A and 2B that share the clinical feature of medullary thyroid carcinoma and pheochromocytoma. MEN 2A mutations involved cysteine residues in the extracellular domain and induced disulfide-linked homodimerization of the Ret protein on the cell surface, leading to activation of its intrinsic tyrosine kinase. On the other hand, a single point mutation in the tyrosine kinase domain was found in MEN 2B, as well as in 30 to 40% of sporadic medullary carcinoma. This mutation also resulted in activation of Ret tyrosine kinase without the formation of its covalent homodimerization. Differences in the mechanisms of ret activation might account for the different phenotypes observed in MEN 2A and MEN 2B. In addition, somatic rearrangement of the ret protooncogene was frequently detected in papillary thyroid carcinoma, particularly from adult Europeans. A recent report demonstrated that the same rearrangement was observed in approximately 60% of papillary carcinomas of children from areas contaminated by the Chernobyl accident, suggesting that ret rearrangement was induced as a direct consequence of radiation exposure. In this review, I focus on the ret mutations detected in thyroid cancer and discuss the mechanisms of its oncogenic activation.

Significance of P53 in human thyroid tumors.

Mutational changes in the p53 tumor suppressor gene are the most frequent genetic alterations in human malignant tumors. Studies have shown a correlation of p53 expression in breast cancer with tumor prognosis. In contrast to mutational activation of ras and GSP in thyroid tumors, little is known about the role of p53 in thyroid tumor development. Therefore thyroid tumors and thyroid tumor cell lines were studied for the presence of p53 mutations. Snap-frozen tissues from 57 differentiated thyroid carcinomas (DTCs) and 5 goiters were studied by immunohistochemical methods. A panel of six antibodies (pAb 240, 421, 1620, 1801, DO7, and CM1) was employed by using the ABC technique. Five cell lines from DTCs (FTC133, 236, 238, PTC337, MTC164) were examined by the same technique. Additionally, genomic DNA from the cells was amplified by the polymerase chain reaction (PCR) and the PCR product studied for p53 mutations (R273H) by mutation-specific oligonucleotide hybridization (MOH) and temperature gradient gel electrophoresis (TGGE) for the p53 exon 8. None of the benign thyroid tumors and 7 of 57 (12%) DTCs strongly express p53 with a heterogeneous distribution in the tumor tissue. All seven patients have metastatic disease or dedifferentiated tumors G3 (three of seven). CM1 was positive in two cell lines (FTC-133, PTC-337), questionable in FTC-238, and negative in FTC-236 and MTC-164. All three follicular cell lines, however, and the original tumor tissue showed the same p53 mutation (R273H) in MOH analysis and TGGE. P53 mutations are rare in thyroid tumors, but the presence of p53 mutations indicates a poor prognosis.(ABSTRACT TRUNCATED AT 250 WORDS)