Pitfalls in thyroid tumour pathology

This review provides an itemized listing of major diagnostic pitfalls in the field of thyroid tumour pathology, emphasizing the features that the authors have found most useful in their recognition and avoidance.     

Manganese superoxide dismutase content and localization in human thyroid tumours

Manganese-containing superoxide dismutase (Mn-SOD) content and its immunohistochemical localization in human thyroid tumours and some other thyroid diseases were examined and compared with adjacent normal thyroid tissue. Enzyme-linked immunosorbent assay (ELISA) was used in this study for the measurement of Mn-SOD. The content of Mn-SOD tended to increase in diffuse hyperplasia, adenomatous goitre, and foliicular adenoma. In papillary carcinoma, it was significantly higher than in adjacent normal thyroid tissue. Foliicular carcinoma also revealed a markedly high Mn-SOD conient. In the immunohistochemicai study, adjaceni normal thyroid tissue showed granular positive staining of Mn-SOD in the cytoplasm. An increase of Mn-SOD was observed in the papillary proliferative lesion of diffuse hyperplasia and in the follicles adjacent to lymphoid tissue in chronic thyroiditis with hypothyroidism. Strong positive staining of Mn-SOD was observed in papillary and foliicular carcinomas, whereas in anaplastic carcinoma staining was markedly less intense. These results indicate that the Mn-SOD content varies according to the degree of differentiation of thyroid carcinomas.     

Thyroid peroxidase and thyroglobulin expression in normal human thyroid glands

The objective of the present study was to investigate thyroid peroxidase (TPO) and thyroglobulin (Tg) expression in normal thyroid tissue. Thirty-eight normal thyroids from fetuses, children, adults, and elderly subjects were evaluated. TPO and Tg expression was determined by analyzing at least 200 cells/specimen. A value of 80% was considered to be the threshold for TPO positivity. In terms of age, TPO expression occurs in fetuses along with follicle differentiation and is absent in solid follicles. TPO staining was cytoplasmic, and was more intense in the apical membrane in tissue from fetuses, children, and young adults. A perinuclear ring was found in tissue from older adults and from the elderly subjects. There was concomitant TPO and Tg expression in all groups studied. Tg expression was observed in all normal thyroids from all age groups. Tg expression was extremely variable (10–100% of the cells) and fainter than TPO expression. Presented at the XXI International Congress of the International Academy of Pathology and 12th World Congress of Academic and Environmental Pathology, Budapest. Hungary, October 20–25, 1996.     

Retinoblastoma and p53 tumour suppressor gene protein expression in carcinomas of the thyroid gland

One hundred and thirty-one thyroid tumours were examined immunohistochemically for expression of retinoblastoma (RB) and p53 protein. The results demonstrate that RB protein is not lost in any cases, indicating that inactivation of the RB gene is unlikely to play a central role in the pathogenesis of thyroid tumours. Eighteen of 24 (75 per cent) undifferentiated carcinomas, 6 of 32 (19 per cent) papillary carcinomas, 5 of 29 (17 per cent) follicular carcinomas, and 6 of 46 (13 per cent) medullary carcinomas showed p53 protein nuclear staining. In 46 per cent of the undifferentiated carcinomas many of the tumour cells had accumulated p53 protein, whereas in the other positive cases less than 5 per cent of the cells had increased p53 protein levels. Our results strongly suggest that p53 protein abnormalities play a crucial role in the progression of well-differentiated to undifferentiated thyroid carcinomas.     

Telomerase activity and telomere length in thyroid neoplasia: biological and clinical implications

Despite several recent studies, the biological status and clinical relevance of telomerase expression in tumours derived from the thyroid follicular cell remain controversial. This study has analysed a series of normal, benign, and malignant thyroid samples using two novel approaches: the use of purified epithelial cell fractions to eliminate false-positives due to telomerase-positive infiltrating lymphocytes; and the simultaneous measurement of telomere length to provide a clearer interpretation of telomere dynamics in thyroid neoplasia. The data obtained support the prediction that the epithelial component of non-neoplastic thyroid and of follicular adenomas is telomerase-negative, any positive results being explicable by lymphocyte infiltration. In contrast, many malignant tumours, both follicular and papillary, were telomerase-positive. However, serial dilution of extracts indicated a wide spectrum of activity in these cancers, possibly related to variation in the proportion of telomerase-positive cells. Furthermore, an unexpectedly high proportion were telomerase-negative, a finding which was not explicable by technical problems such as TRAP (telomeric repeat amplification protocol) assay sensitivity. Many of these apparently telomerase-negative tumours had abnormally long telomeres. Correlation of telomerase and telomere length data suggests that thyroid cancers fall into three biological groups: telomerase-positive lesions, consistent with the conventional model of telomere erosion followed by telomerase reactivation; telomerase-negative tumours, which maintain telomere length by a mechanism independent of telomerase; and telomerase-negative tumours which are still undergoing telomere erosion and may therefore be composed of mortal cancer cells. From a clinical standpoint, it is concluded that telomerase detection on unfractionated tissue, such as fine needle aspirates, is of no value as a marker of malignancy in follicular lesions, due to both low sensitivity and specificity.     

Expression of prolactin receptor and prolactin in normal and malignant thyroid: A tissue microarray study

Objective There is increasing evidence involving prolactin (PRL) and its receptor (PRLR) in the development of different cancers. The aim of the present study was to investigate the expression of PRLR and PRL in human thyroid tissues. Design and Methods Using tissue microarray (TMA) by immunohistochemical staining, we examined the expression level of PRLR and PRL in 314 specimens from 71 thyroid cancer patients and 15 normal thyroid samples. Results Expression of the PRLR was observed in 93.3% of normal thyroid samples and in 76.1% of all thyroid cancers, while expression of PRL was observed in only 10% of medullary thyroid carcinomas and not at all in the other specimens, whether normal or neoplastic. Moreover, results suggested an overexpression of PRLR in 70% of medullary thyroid carcinomas, whereas 53.3% of poorly differentiated thyroid carcinomas showed a negative pattern of staining (p=0.014 vs normal). Conclusions Present data revealed, for the first time, a widespread expression of PRLR in normal and neoplastic human thyroid tissues as well as a scarce expression of PRL, observed only in a few medullary thyroid carcinomas. Whether the overexpression of PRLR observed in medullary thyroid carcinomas or the underexpression of PRLR observed in poorly differentiated thyroid carcinomas play a contributory role in the oncogenesis of these tumors remains to be determined.     

Expression of somatostatin mRNA and peptides in C-cell tumours of the thyroid gland in Han Wistar rats

C-cell tumours of the thyroid gland are among the most common spontaneous neoplasms of the laboratory rat. With the exception of calcitonin, little attention has been paid to the secretory peptides of C cells during the development of neoplasia. Of these peptides, somatostatin (SS) is of particular interest because it has been shown to have a direct anti-secretory effect on both thyroid follicular and C cells in vitro. In the present study, in situ hybridization and immunohistochemistry were used to investigate the expression of SS mRNA and SS peptides, in normal C cells and a range of spontaneous proliferative C-cell lesions in the Han Wistar rat. It was confirmed that a small minority of C cells in the normal rat thyroid gland produce and store SS peptides; however, approximately half of all C-cell adenomas and C-cell carcinomas stained positively for SS mRNA and peptides. SS expression was also observed in all metastatic deposits of carcinomas in drainage lymph nodes. From these observations, it appears that C-cell tumours are more likely to develop from SS-expressing stem cells, rather than from non-SS-expressing stem cells. In addition, a lack of differentiation of neoplastic C cells, or reversion to more primitive cell types, could account for increased number of cells expressing SS in C-cell tumours relative to the normal C-cell population. Finally, the mean percentage of cells that stained positively for SS mRNA and peptides appeared to be significantly higher in small C-cell tumours, suggesting that SS may have exerted a growth-controlling influence on these lesions.     

Heterotopic intrathymic thyroid tissue

Heterotopic intrathymic thyroid tissue is an extremely rare condition, but it is important to distinguish it from metastases of clinically undetected thyroid carcinoma because metastatic papillary thyroid carcinoma is often so well differentiated, simulating normal thyroid tissue. Described herein are histological findings of heterotopic intrathymic thyroid tissue that was incidentally identified in a woman with papillary thyroid carcinoma during histological examination of a radical neck dissection specimen. These findings emphasize that this rare incidence may occur and should be differentiated from metastatic papillary carcinoma. Histologically, the patient's intrathymic thyroid follicles were identical to the normal thyroid follicles, having flat cuboidal cells with uniformly small nuclei without nuclear grooves or inclusions. The follicular cells had a low Ki-67 labeling index close to zero, and immunonegativity for galectin-3, HBME-1, and RET oncoprotein, in contrast to the tumor cells in primary papillary thyroid carcinoma of the patient. To the authors' knowledge this is the first case report of intrathymic heterotopic thyroid tissue posing a diagnostic difficulty in a patient with papillary thyroid carcinoma.     

Thyrocyte integration, and thyroid folliculogenesis and tissue regeneration: Perspective for thyroid tissue engineering

The thyroid gland is composed of many ball-like structures called thyroid follicles, which are supported by the interfollicular extracellular matrix (ECM) and a capillary network. The component thyrocytes are highly integrated in their specific structural and functional polarization. In conventional monolayer and floating culture systems, thyrocytes cannot organize themselves into follicles with normal polarity. In contrast, in 3-D collagen gel culture, thyrocytes easily form stable follicles with physiological polarity. Integration of thyrocyte growth and differentiation results ultimately in thyroid folliculogenesis. This culture method and subacute thyroiditis are two promising models for addressing mechanisms of folliculogenesis, because thyroid-follicle formation actively occurs both in the culture system and at the regenerative phase of the disorder. The understanding of the mechanistic basis of folliculogenesis is prerequisite for generation of artificial thyroid tissue, which would enable a more physiological strategy to the treatment of hypothyroidism caused by various diseases and surgical processes than conventional hormone replacement therapy. We review here thyrocyte integration, and thyroid folliculogenesis and tissue regeneration. We also briefly discuss a perspective for thyroid tissue regeneration and engineering.     

Expression of multidrug resistance-associated protein 2 (MRP2) in normal human tissues and carcinomas using tissue microarrays

AIMS: Using tissue microarrays, this study analysed the expression of the multidrug resistance protein, MRP2, by immunohistochemistry with two different MRP2 antibodies. This is the first study to address the expression of MRP2 in various common human neoplasms. METHODS AND RESULTS: Immunohistochemistry was performed on zinc formalin-fixed tissue to evaluate normal tissues and carcinomas using two antibodies against MRP2 (EAG5, a polyclonal antibody, and M2-lll-6, a monoclonal antibody). Immunostaining was localized in neoplastic cells mainly on the cell membrane with M2-lll-6 and cell membrane and cytoplasm with EAG5. In normal tissues MRP2 was expressed in liver, gastrointestinal tract, and kidney tubular epithelial cells with both antibodies. MRP2 was seen in nine of 22 renal cell carcinomas, eight of 13 gastric carcinomas, 25 of 49 breast carcinomas, 14 of 32 lung carcinomas, 39 of 50 colon carcinomas, and 16 of 17 ovarian carcinomas. There was < 10% variability between the two antibodies. MRP2 expression was highest in moderate to poorly differentiated tumours from colon, lung, gastric, and ovarian carcinomas and in grade 2 and 3 breast and renal carcinomas. CONCLUSION: The expression of MRP2 in many solid human tumours indicates that inherent drug resistance may play an important role as a biomarker for predictive chemotherapy treatment.     

Prevalence of thyroid cancer at a medical screening center: pathological features of screen-detected thyroid carcinomas

Purpose

To assess the incidence of thyroid malignancy in an adult population screened by high-resolution ultrasonography at a medical screening center and to compare the clinical and pathological features of screen-detected thyroid carcinomas to symptomatic overt thyroid carcinomas.

Materials and Methods

We calculated the prevalence of screen-detected thyroid cancer at a medical screening center using high-resolution ultrasonography and fine needle aspiration. We then compared the clinical and pathological features of screen-detected thyroid cancers (n = 46) to clinical symptomatic thyroid cancers (n = 157). We evaluated age, gender, size, perithyroidal extension, lymphovascular extension, stage, histological lymph node metastasis, and the type of cancer. We also compared the above findings of micropapillary carcinomas to papillary thyroid carcinomas that were larger than 1 cm in diameter.

Results

Screen-detected thyroid nodule patients were 2,747 (37%) of 7,491 patients. Nodules selected for fine needle aspiration were 658 and cytology confirmed malignancy were 79 (12%) nodules. When screen-detected thyroid cancers (n = 46) were compared to symptomatic overt thyroid cancers (n = 157), only statistically significant factor was size (p = 0.002). Papillary thyroid carcinomas that were larger than 1 cm had more frequent capsular invasion (p = 0.000) and a higher stage (p = 0.027), and a higher prevalence of lymph node metastases (p = 0.002).

Conclusion

Screen-detected thyroid cancers should be managed as same as symptomatic thyroid cancers in respect to size, and an assessment should strictly be based on the ultrasound features and fine needle aspiration biopsy findings.     

Molecular pathology of thyroid tumours of follicular cells: a review of genetic alterations and their clinicopathological relevance

Thyroid cancer is the most common endocrine malignancy. Knowledge of the molecular pathology of thyroid tumours originating from follicular cells has greatly advanced in the past several years. Common molecular alterations, such as BRAF p.V600E, RAS point mutations, and fusion oncogenes (RET–PTC being the prototypical example), have been, respectively, associated with conventional papillary carcinoma, follicular‐patterned tumours (follicular adenoma, follicular carcinoma, and the follicular variant of papillary carcinoma/non‐invasive follicular thyroid neoplasm with papillary‐like nuclear features), and with papillary carcinomas from young patients and arising after exposure to ionising radiation, respectively. The remarkable correlation between genotype and phenotype shows how specific, mutually exclusive molecular changes can promote tumour development and initiate a multistep tumorigenic process that is characterised by aberrant activation of mitogen‐activated protein kinase and phosphoinositide 3‐kinase–PTEN–AKT signalling. Molecular alterations are becoming useful biomarkers for diagnosis and risk stratification, and as potential treatment targets for aggressive forms of thyroid carcinoma. What follows is a review of the principal genetic alterations of thyroid tumours originating from follicular cells and of their clinicopathological relevance.     

Tissue polypeptide antigen in thyroid tumours of follicular cell origin: an immunohistochemical re-evaluation for diagnostic purposes

Using immunoperoxidase procedures on paraffin sections, we have investigated the distribution pattern of tissue polypeptide antigen (TPA) in follicular adenomas, (20 cases), follicular carcinomas (23 cases), papillary carcinomas (10 cases), anaplastic carcinomas (eight cases) and medullary carcinomas (four cases). Normal thyroid tissue surrounding adenomas was also tested as a control. Our results document positivity for TPA in follicular, papillary and medullary carcinomas, whereas no reactivity was encountered in follicular adenomas and anaplastic carcinomas. These immunohistochemical data were compared with serological levels of TPA and the findings were discordant only for anaplastic carcinomas. We contend that the demonstration of TPA, possible in alcohol- or formalin-fixed tissues, may prove to be of value in the differential diagnosis of thyroid adenomas from carcinomas of follicular cell origin.