A comparative study of flow cytometry and histopathologic findings in thyroid follicular carcinomas and adenomas

Genomic differences in benign and malignant follicular thyroid tumours using 1-Mb array-comparative genomic hybridisation

Currently there is a lack of objective markers that can reliably differentiate benign and malignant follicular thyroid tumours. Such markers are needed to avoid the morbidity and cost of diagnosing these lesions by a thyroid lobectomy and then a second operation to remove the remaining half of thyroid if cancer is found. The aim of this research was to look for genomic markers that might solve this important problem. Ethical approval for the project was obtained. DNA was extracted from formalin-fixed paraffin-embedded specimens and copy number analysed using an in-house produced 1-megabase genomic array by comparative genomic hybridization (1Mb-aCGH). Acceptable quality data were obtained in 25/26 (96 %) of adenomas and 17/28 (61 %) of carcinomas. Among the carcinomas, 11 were minimally invasive (MI), 5 widely invasive (WI) and there was one metastasis. Recurrent copy number changes distinguishing benign and malignant included +1p34.2-36.33, +1q, +13q12.11-14.3, +14q22.1-32.33, +20q and -22. +20q became more sensitive (36.4 %) for MI carcinomas, whereas +13q12.11-14.3 and +14q22.1-32.33 became more sensitive (66.7 %) for identifying WI cancers from adenomas. Only in the context of aneuploidy (3 adenomas, 3 MI, 3 WI) there were some specific copy number changes that could differentiate all aneuploid adenomas from carcinomas. This research is the first using 1Mb-aCGH to study benign and malignant follicular thyroid tumours. Overall, the incidence of any copy number changes is low, but there are a number of changes associated with different tumour types. Further research with a larger sample and better quality DNA will clarify these findings.

Molecular pathogenesis of follicular cell derived thyroid cancers

Thyroid cancers are the most common endocrine malignancy. Radiation exposure, family history of thyroid cancer and some inherited conditions are the most important predisposing factors for the development of thyroid cancer. Three mitogenic signalling pathways have been described in the thyroid cell, which are influenced by various stimulatory and inhibitory hormones, growth factors and neurotransmitters. Various proto-oncogenes and oncogenes like ras, braf, trk, met and RET also play a role in the signal transduction systems. Two theories have been described in thyroid cancer pathogenesis, the foetal cell carcinogenesis theory and the more common, multistep carcinogenesis theory. The multistep carcinogenesis theory is now the accepted model in many human cancers, including thyroid cancer. The early events of tumour formation are the consequence of activation of either various growth factors or the proto-oncogenes like ras, met or ret. This results in the formation of differentiated thyroid cancers like the papillary, follicular or Hurthle cell cancers. The later stages of tumour formation involve further activation of proto-oncogenes and loss or inactivation of tumour suppressor genes like p53. Based on this theory, follicular carcinomas are generated from follicular adenomas and papillary carcinomas from precursor cells generated from thyrocytes. Anaplastic carcinoma may develop from papillary or follicular carcinoma by dedifferentiation. In this review article, we highlight the molecular pathogenesis of thyroid tumours.

Aneuploidy and RAS mutations are mutually exclusive events in the development of well-differentiated thyroid follicular tumours

OBJECTIVE

Follicular thyroid tumours present several genetic alterations such as aneuploidy, RAS mutations and PAX8/PPARgammarearrangements. The molecular basis of aneuploidy remains undefined in the majority of human cancers. It has been proposed that mutations in RAS oncogenes could be related to chromosomal instability, although this issue remains controversial. The aim of our study was to investigate the correlation between aneuploidy, RAS mutations and PAX8/PPARgamma gene rearrangement in thyroid follicular tumours.

DESIGN

Ploidy status was determined by flow cytometry in 111 thyroid lesions (42 follicular thyroid adenomas, 27 follicular thyroid carcinomas, 19 follicular variants of papillary thyroid carcinoma, 20 poorly differentiated thyroid carcinomas and 3 anaplastic thyroid carcinomas). RAS mutations and PAX8/PPARgamma fusion gene were investigated in 101 and 87 of these samples, respectively.

RESULTS

Altogether, 12 of 50 (24%) diploid tumours presented RAS mutation which contrasts with 3 of 51 (5.9%; P = 0.0124) RAS mutations in the group of aneuploid tumours. The aneuploid tumours harbouring RAS mutations were two poorly differentiated carcinomas and one follicular variant of papillary thyroid carcinoma with poorly differentiated areas. None of the tumours with RAS mutations expressed the PAX8/PPARgamma fusion gene. Three of five (60%) follicular thyroid adenomas and 1 of 7 (14%) follicular thyroid carcinomas, with the PAX8/PPARgamma fusion gene, were aneuploid.

CONCLUSIONS

Our data suggest that aneuploidy and RAS mutations are mutually exclusive events in the development of well-differentiated thyroid follicular tumours.

Fine-needle aspiration of the thyroid: an overview

Thyroid nodules (TN) are a common clinical problem. Fine needle aspiration (FNA) of the thyroid now is practiced worldwide and proves to be the most economical and reliable diagnostic procedure to identify TNs that need surgical excision and TNs that can be managed conservatively. The key for the success of thyroid FNA consists of an adequate or representative cell sample and the expertise in thyroid cytology. The FNA cytologic manifestations of TNs may be classified into seven working cytodiagnostic groups consisting of a few heterogenous lesions each to facilitate the differential diagnosis. Recent application of diagnostic molecular techniques to aspirated thyroid cells proved to be useful in separating benign from malignant TNs in several cases of indeterminate lesions.

Fractal dynamics in the differential diagnosis of thyroideal follicular neoplasms

In this study, we investigated the sensitivity, specificity, and predictive values of morphometric parameters of thyroideal follicular neoplasms based on concepts of fractal geometry. Thirty-seven follicular adenomas and 36 well-differentiated follicular carcinomas were assessed morphometrically. The nuclear area, nuclear area fraction, nuclear regularity factor, nuclear elongation factor, and slope setting (representing the ratio between the nuclear perimeter and nuclear regularity factor) were subjected to fractal dimensions analysis. By univariate analysis, the nuclear area, nuclear area fraction, nuclear regularity factor and slope values discriminate between adenomas and carcinomas. By multivariate analysis, the nuclear area, nuclear area fraction and slope values possess significant discriminatory powers in distinguishing between adenomas and carcinomas. Incorporating the nuclear area, nuclear area fraction, and slope values leads to a discriminatory power with 92% specificity and 83% sensitivity. The reciprocal relationships between the nuclear area, nuclear perimeter, and nuclear regularity factor of the cells of thyroideal adenomas and carcinomas may be expressed by fractal dimensions. Analysis limited to one parameter provides incomplete data. Expressing variations of the nuclear perimeter as a function of the nuclear regularity factor, the slope values constitute an independent attribute that significantly differentiates thyroideal adenomas from carcinomas.

Minireview: branded from the start-distinct oncogenic initiating events may determine tumor fate in the thyroid

Thyroid follicular neoplasms commonly have aneuploidy, presumably due to chromosomal instability. This property is associated with a greater malignant potential and worse prognosis. Recently, there has been considerable progress in our understanding of mechanisms that may account for chromosomal instability in cancer cells. Many tumors with chromosomal instability have abnormalities in the cell cycle checkpoint that monitors the fidelity of mitosis. Mutations of Bub1 or BubR1, genes coding for kinases involved in mitotic spindle assembly checkpoint signaling, are found in a small subset of aneuploid tumors. Other components of protein complexes responsible for attachment of kinetochores to microtubules, or for cohesion between sister chromatids, may also be subject to alterations during tumor progression. Here, we also discuss the evidence that certain oncogenic events, such as Ras mutations, may predispose cells to chromosomal instability by favoring inappropriate posttranslational changes in mitotic checkpoint components through activation of upstream kinases during tumor initiation or progression.

Mechanisms of aneuploidy in thyroid cancer cell lines and tissues: evidence for mitotic checkpoint dysfunction without mutations in BUB1 and BUBR1

OBJECTIVE

Thyroid follicular adenomas (FA) and carcinomas (FC) have a high prevalence of aneuploidy. We examined the contribution of mitotic checkpoint dysfunction and mutations of BUB1 or BUBR1, components of the spindle assembly checkpoint pathway, to chromosomal instability in thyroid cancer.

DESIGN

The integrity of the mitotic checkpoint was studied in 8 aneuploid thyroid tumour cell lines. All cell lines as well as 9 FA, 9 FC, and 1 aneuploid papillary carcinoma were screened for mutations of BUB1 by SSCP and direct sequencing. Cell lines were also examined for mutations of BUBR1.

RESULTS

Neither FRO, NPA nor WRO cells arrested in mitosis after treatment with nocodazole, whereas other aneuploid cell lines paused appropriately following microtubule disruption. One FC had a 2-bp somatic deletion (G2480/A2481) of BUB1 leading to a frameshift, and one FC had a silent polymorphism at nucleotide 1049 (TGT-TGC). There was a silent polymorphism of BUBR1 (G1271A) in one sample.

CONCLUSION

Some, but not all thyroid cancer cell lines with aneuploidy have an abnormal mitotic checkpoint, indicating that chromosomal instability may arise through alternative cell cycle defects. Moreover, mutations of BUB1 or BUBR1 are infrequent in follicular neoplasms, and do not account for aneuploidy in thyroid cancer.

Genetic markers in thyroid neoplasia

Cancer is a disease of genes. Detection of genetic abnormalities associated with cancers of various cell types can now be used for genetic counseling, diagnosis or treatment selection. In the case of thyroid cancer, genetic testing for mutations of the RET oncogene has had a profound effect on the management of medullary thyroid carcinomas. There is also considerable information on the genetic changes associated with development and progression of cancers of thyroid follicular cells, although these have not yet proven to be of practical value for clinical diagnosis or to guide prognosis and therapy.

A clinicopathologic study of minimally invasive follicular carcinoma of the thyroid gland with a review of the English literature

BACKGROUND

The criteria for minimally invasive (low grade) follicular carcinoma of the thyroid (MI) remain controversial, often resulting in unnecessary treatment.

METHODS

The records of 130 patients with minimally invasive (MI) follicular thyroid carcinoma were retrieved from the files of the Endocrine Tumor Registry of the Armed Forces Institute of Pathology.

RESULTS

Ninety-five patients were confirmed to have MI based on the authors' criteria of small-to-medium vessel invasion, capsular invasion of up to full thickness, no parenchymal tumor extension, and no tumor necrosis (patients with oxyphilic tumors were excluded). The remaining 35 patients had tumors that were reclassified as "not low grade" based on large vessel invasion, extension into parenchyma, and tumor necrosis (oxyphilic cases excluded). The MI patients included 67 women and 28 men, ages 20-95 years (average, 42.0 years). Nearly all patients presented with a thyroid mass (n = 90 patients). The mean tumor size was 2.8 cm. Histologic features examined for tumor classification included cellularity, capsule nature, capsular invasion, vascular invasion, extension into parenchyma, cytoplasmic oxyphilia, mitotic activity, and necrosis. All patients were treated with surgical excision. Adjuvant radioactive iodine therapy was performed in 24 patients. Five patients developed recurrent disease: four were alive or had died without evidence of disease after additional treatment (mean, 18.1 years), and one patient died with disease (MI tumor) at 15.1 years. All of the remaining patients were disease free (mean follow-up, 16.5 years).

CONCLUSIONS

There are reproducible histologic criteria to diagnose patients with MI follicular carcinoma. The overall excellent long term prognosis and a good patient outcome suggests that no additional surgery is necessary.

The value of histomorphometric nuclear parameters in the diagnosis of well differentiated follicular carcinomas and follicular adenomas of the thyroid gland

AIMS

To explore the potential of histomorphometric analysis in distinction between follicular adenomas and well differentiated follicular carcinomas of the thyroid gland. Their differentiation on routine histological study may be a challenging exercise, being contingent upon the absence or presence of vascular invasion and penetration of neoplastic follicles through the capsule of the tumour.

METHODS AND RESULTS

Computer-assisted image analysis was performed to gauge the nuclear area, nuclear Ferret diameter, nuclear regularity factor, nuclear elongation factor, number of nuclear vesicles and total area of all nuclear vesicles in the follicles of 37 adenomas and 36 well differentiated carcinomas. By univariate analysis, these nuclear descriptors (with the exception of the elongation factor) were found to correlate with the benign or malignant nature of the tumours. By multivariate analysis, only the nuclear area, Ferret diameter and regularity factor were ascertained to be significant predictors of malignancy. A fitted logit model correctly predicted 91% of the cancers and 87% of the adenomas.

CONCLUSIONS

Histomorphometrically gauged nuclear parameters of the tumour cells may reinforce pathologists' decision-making by adding objective and unbiased criteria to their subjective assessment of follicular neoplasms in cases in which vascular or capsular invasion are not detected.

Characteristics of multicellular spheroids formed by primary cultures of human thyroid tumor cells

Features of multicellular tumor spheroids (MCTS) differed depending on their types of cells. MCTS formed by 4000 human thyroid primary culture epithelial tumor cells displayed diameters between 0.31 and 0.33 mm within 2 days regardless of the stage of malignancy of the originating tumors. Their cellular composition reflected that of the originating tumor in regard to DNA content and the expression of cytokeratin, vimentin, as well as thyroglobulin. During the following 3 weeks, their sizes increased up to diameters of 0.42 mm when their cells had been derived from carcinomas, and MCTS originating from adenomas stopped growing within the next 2 days. After 8 days of incubation, proliferating cells were only found in carcinoma MCTS. The cells were randomly distributed over the total volume of the spheroids, which displayed irregular cell arrangements but not concentric cell layers and did not form necrotic centers.