Inherited Follicular Epithelial-Derived Thyroid Carcinomas: From Molecular Biology to Histological Correlates

Cancer derived from thyroid follicular epithelial cells is common; it represents the most common endocrine malignancy. The molecular features of sporadic tumors have been clarified in the past decade. However the incidence of familial disease has not been emphasized and is often overlooked in routine practice. A careful clinical documentation of family history or familial syndromes that can be associated with thyroid disease can help identify germline susceptibility-driven thyroid neoplasia. In this review, we summarize a large body of information about both syndromic and non-syndromic familial thyroid carcinomas. A significant number of patients with inherited non-medullary thyroid carcinomas manifest disease that appears to be sporadic disease even in some syndromic cases. The cytomorphology of the tumor(s), molecular immunohistochemistry, the findings in the non-tumorous thyroid parenchyma and other associated lesions may provide insight into the underlying syndromic disorder. However, the increasing evidence of familial predisposition to non-syndromic thyroid cancers is raising questions about the importance of genetics and epigenetics. What appears to be "sporadic" is becoming less often truly so and more often an opportunity to identify and understand novel genetic variants that underlie tumorigenesis. Pathologists must be aware of the unusual morphologic features that should prompt germline screening. Therefore, recognition of harbingers of specific germline susceptibility syndromes can assist in providing information to facilitate early detection to prevent aggressive disease.

Thyroid Hürthle cell tumors: research of potential markers of malignancy

INTRODUCTION

Hurthle cell tumors (HCTs) are rare thyroid neoplasia. To date, capsular and/or vascular invasion are the only findings predicting malignancy. Recently, mutation of 19p13, encoding two proteins involved in cell proliferation and apoptosis (GRIM-19 and p19), has been described. The aim of our study is to evaluate the cellular proliferation index (Ki67), GRIM-19 and p19 expression as diagnostic markers of malignancy in HCT.

MATERIALS AND METHODS

Eighty patients with HCT (32 carcinomas, 48 adenomas) whom underwent surgery in our center were included. Samples of both neoplastic lesions and adjacent normal thyroid tissue were analyzed by means of tissue micro-arrays. Correlations between expressions of Ki67, GRIM-19 and p19 and final histology were analyzed.

RESULTS

Mean size of the lesion was higher in carcinomas than in adenomas (p = 0.01). GRIM-19 and p19 were significantly underexpressed in Hurthle cells tumors compared to normal tissue (p = 0.0004 and p = 0.0001, respectively). Ki67 and GRIM-19 were, respectively, higher and down-expressed in carcinomas compared to adenomas (p = 0.0004 and p = 0.005, respectively). On multivariate analysis, size correlates with carcinoma diagnosis. Neither GRIM-19 nor Ki67 index was related to size. The expression of p19 was reduced in both adenoma and carcinoma but differences were not statistically significant (p = 0.13).

CONCLUSIONS

Our study suggest that Ki67 and GRIM-19 correlate with malignancy in HCT. The expression of p19 is down-regulated in HCT, but it is not diagnostic of carcinoma. Ki67 and GRIM-19 may potentially help as cytological markers of malignancy in HCT.

The biology and the genetics of Hurthle cell tumors of the thyroid

The biology and the genetics of Hürthle cell tumors are reviewed starting from the characterization and differential diagnosis of the numerous benign and malignant, neoplastic and nonneoplastic lesions of the thyroid in which Hürthle cell transformation is frequently observed. The clinicopathologic and molecular evidence obtained from the comparative study of the aforementioned conditions indicate that Hürthle cell appearance represents a phenotype that is superimposed on the genotypic and conventional histopathologic features of the tumors. Hürthle cell tumors differ from their non-Hürthle counterparts regarding the prevalence of large deletions of mitochondrial DNA (mtDNA), mutations of mtDNA genes coding for oxidative phosphorylation (OXPHOS) proteins (namely mutations of complex I subunit genes) and mutations of nuclear genes coding also for mitochondrial OXPHOS proteins. Such mitochondrial alterations lead to energy production defects in Hürthle cell tumors; the increased proliferation of mitochondria may reflect a compensatory mechanism for such defects and is associated with the overexpression of factors involved in mitochondrial biogenesis. The mitochondrial abnormalities are also thought to play a major role in the predisposition for necrosis instead of apoptosis which seems to be blocked in most Hürthle cell tumors. Finally, the results obtained in experimental models using cybrid cell lines and the data obtained from histopathologic and molecular studies of familial Hürthle cell tumors are used, together with the aforementioned genetic and epigenetic alterations, to progress in the understanding of the mechanisms through which mitochondrial abnormalities may be involved in the different steps of thyroid carcinogenesis, from tumor initiation to metastization.