Absence of the BRAF and the GRIM-19 mutations in oncocytic (Hürthle cell) solid cell nests of the thyroid

Oncocytic Change in Thyroid Pathology

Oncocytes are cells that have abundant eosinophilic cytoplasm due to the accumulation of mitochondria; they are also known as oxyphils. In the thyroid they have been called Hürthle cells but this is a misnomer, since Hürthle described C cells; for this reason, we propose the use of "oncocyte" as a scientific term rather than an incorrect eponym. Oncocytic change occurs in nontumorous thyroid disorders, in benign and malignant tumors of thyroid follicular cells, in tumors composed of thyroid C cells, and intrathyroidal parathyroid proliferations as well as in metastatic lesions. The morphology of primary oncocytic thyroid tumors is similar to that of their non-oncocytic counterparts but also is complicated by the cytologic features of these cells that include both abundant eosinophilic cytoplasm and large cherry red nucleoli. The molecular alterations in oncocytic thyroid tumors echo those of their non-oncocytic counterparts but in addition feature mitochondrial DNA mutations as well as chromosomal gains and losses. In this review we emphasize the importance of recognition of the spectrum of oncocytic thyroid pathology. The cell of origin, morphologic features including architecture, nuclear atypia and invasive growth, as well as high grade features such as mitoses and necrosis, enable accurate classification of these lesions. The molecular alterations underlying the pathological entity are associated with genetic alterations associated with oncocytic change. The arbitrary cut-off of 75% oncocytic change to classify a lesion as an oncocytic variant brings another complexity to the classification scheme of tumors that frequently have mixed oncocytic and non-oncocytic components. This controversial and often confusing area of thyroid pathology requires thoughtful and cautious investigation to clarify accurate diagnosis, prognosis and prediction for patients with oncocytic thyroid lesions.

Positivity for GATA3 and TTF-1 (SPT24), and Negativity for Monoclonal PAX8 Expand the Biomarker Profile of the Solid Cell Nests of the Thyroid Gland

Solid cell nests (SCNs) are usually distinguished on conventional H&E-stained sections; however, the morphological heterogeneity in SCNs and hyperplasia of these ultimobranchial body remnants can mimic other diagnostic entities including but not limited to papillary microcarcinoma. In order to confirm the thyroid follicular epithelial origin and exclude the possibility of SCNs, most diagnosticians use immunohistochemical biomarkers of thyroid follicular epithelial cells and/or those of SCNs. While the expression profile of monoclonal PAX8 has not been reported previously in SCNs, the status of TTF-1 expression using the 8G7G3/1 clone has been inconsistent among several studies. Given the potential diagnostic pitfalls, this series investigated the expression profile of GATA3, monoclonal PAX8, and TTF-1 (SPT24), along with p63, p40, monoclonal calcitonin, monoclonal CEA, and HBME-1 in a tissue microarray (TMA) of 56 SCNs. SCNs were all diffusely and strongly positive for TTF-1 (SPT24), p63, and p40, and were negative for monoclonal PAX8 and calcitonin. Positivity for GATA3 and monoclonal CEA was identified in 41 (73.2%) and 36 (64.3%) of SCNs. In addition, 18 (32.1%) SCNs displayed HBME-1 reactivity. These findings expand the immunohistochemical correlates of SCNs by demonstrating positivity for GATA3 and TTF-1 (SPT24), and negativity for monoclonal PAX8. The identification of monoclonal CEA expression and HBME-1 in SCNs also underscores the limitations of these select biomarkers in the distinction of C cell proliferations and papillary microcarcinoma, respectively. The findings of this series also suggest that positivity for TTF-1 (SPT24) alone should not be used to confirm the thyroid follicular epithelial origin. Therefore, the combined use of TTF-1 (SPT24) and monoclonal PAX8 in association with p63 or p40 provides an accurate distinction of SCNs.

Solid cell nests of the thyroid gland: morphological, immunohistochemical and genetic features

AIMS

The correct identification of solid cell nests (SCNs) is an important issue in thyroid pathology because of the spectrum of differential diagnoses of this type of lesion.

METHODS AND RESULTS

Ten cases of 295 consecutive thyroidectomies showed the presence of SCNs at histological examination. The identification of the exact SCN type required the distinction of the cystic and solid pattern; SCNs were usually composed of a mixture of main cells (MCs) and C-cells (CCs). The immunohistochemical calcitonin stain identified CCs easily, both inside SCNs and dispersed in islets at the periphery. For the characterization of MCs, we added the utility of p40 to p63. The use of thyroid transcription factor-1 (TTF-1) helped in their identification, as MCs did not react with this marker; the combination of TTF-1 and p40 or p63 IHC stains was useful for the characterization of cystic SCNs of both types 3 and 4. The negativity of mouse monoclonal mesothelioma antibody (HMBE-1) and a very low proliferative index (MIB-1) supported the diagnosis. [Correction added on 23 November 2015, after online publication: MIB-1 was incorrectly defined, the expanded form was deleted.] We discourage the use of galectin-3 (Gal-3) and cytokeratin-19 (CK-19), as they have an important overlap with papillary thyroid carcinoma. The complete absence of any B-Raf proto-oncogene, serine/threonine kinase (BRAF) mutations is an additional fundamental finding.

CONCLUSIONS

We reviewed the most relevant morphological and immunohistochemical features of SCNs and have provided a genetic analysis of the BRAF gene because of its expanding use in thyroid pathology.

Adrenocortical oncocytoma presenting as Cushing's syndrome: an additional report of a paediatric case

Oncocytomas are tumours predominantly or exclusively composed of oncocytes, cells with granular and eosinophilic cytoplasm filled with mitochondria. Although they can occur in every organ, they are rare in adrenal glands, and in paediatric patients they are even rarer, with only three case reports previously published. We present a preschool child developing Cushing's syndrome due to an adrenocortical oncocytoma, which was confirmed immunohistochemically with antibodies to the mitochondrial electron complex 2. A 5.8-year-old girl presented with clinical features of Cushing's syndrome. ACTH-independent hypercortisolism was confirmed biochemically and a left adrenal mass was detected by imaging and removed by laparotomy. Histopathological analysis revealed a tumour composed of more than 95 % of oncocytes, confirmed immunohistochemically with antibodies to subunits A and B of the mitochondrial enzyme succinate dehydrogenase. Using the Lin-Weiss-Bisceglia score system and the reticulin algorithm, this tumour was categorized as a benign adrenocortical oncocytoma. The patient currently has 64 months of follow-up, without any evidence of relapse of symptoms. To our knowledge, we herein present the youngest patient developing an adrenocortical oncocytoma and the first manifestation of Cushing's syndrome due to this rare neoplasm in paediatric patients. We also emphasize the clinical usefulness of immunohistochemistry to the mitochondrial enzyme succinate dehydrogenase to confirm the oxyphilic nature of adrenocortical oncocytomas.

The diagnosis and treatment of oncocytic carcinoma

The purpose of this study was to assess the diagnosis, treatment, and prognosis of oncocytic carcinoma. This was a retrospective study of 7 patients with oncocytic carcinoma according to the 2005 World Health Organization classification guidelines who underwent 1 or more surgical interventions within the last 20-year period from 1992 to 2012. The lesions were located in the parotid glands in 5 patients, the submandibular glands in 1 patient, and the sublingual gland in 1 patient. One of the patients experienced tumor recurrence after conservative surgery before he was admitted to our department. Five patients were treated with a total parotidectomy, and 3 underwent additional neck dissection. Only 1 patient died, as a result of pulmonary metastases. After a follow-up period of 3 to 198 months, no recurrences were found in any of the surviving patients. On the basis of our experience, poorly differentiated oncocytic carcinoma should be treated with the total resection of the affected salivary gland and a selective neck dissection. Patients with oncocytic carcinoma should remain in long-term follow-up.

Ectopic thyroid tissue in the adrenal gland: a report of two cases with pathogenetic implications

BACKGROUND

Ectopic thyroid tissue is usually found anywhere along the embryonic descent pathway of the medial thyroid anlage from the tongue to the trachea (Wölfler area). However, ectopic thyroid tissue in the adrenal gland (ETTAG) is not easy to understand on the basis of thyroid embryology; because it is so rare, the possibility of metastasis should first be considered. Here, we describe two cases of ETTAG with pathogenetic implications and review the associated literature.

PATIENT FINDINGS

Two cases of ETTAG presented as incidental cystic adrenal masses in adult females, one having a congenital hernia of Morgagni. The ETTAG was histologically indistinguishable from normal orthotopic thyroid tissue, and its follicular nature was confirmed by immunohistochemical positivity for thyroglobulin, thyroperoxidase, thyroid transcription factor-1 (TTF-1/Titf-1/Nkx2.1), cytokeratin AE1/AE3, cytokeratin 7, pendrin, human sodium iodide symporter, paired box gene 8, and forkhead box E1 (TTF-2), as well as positivity for the messenger RNA of the thyroglobulin gene by in situ hybridization analysis. No C cells (negativity for calcitonin, chromogranin, and synaptophysin) were present. Neither BRAF nor KRAS mutations were detected with real-time polymerase chain reaction analysis. Further work-up did not show evidence of thyroid malignancy.

SUMMARY

ETTAG is a rare finding, with only seven cases reported; women are much more frequently affected than men (8:1), and it usually presents in the fifth decade (mean age 54, range 38-67) as a cystic adrenal mass incidentally discovered on abdominal ultrasonography and/or in computed tomography images. ETTAG is composed of normal follicular cells without C cells. The expression of some transcription factors (TTF-1, paired box gene 8, and FOXE1) involved in development and/or migration of the medial thyroid anlage is preserved. Coexistence of a congenital hernia of Morgagni in one patient suggests an overdescent of medial thyroid anlage-derived cells in its pathogenesis.

CONCLUSION

Although ETTAG pathogenesis remains unknown, the lack of C cells together with the coexistence of a congenital defect of the anterior diaphragm (hernia of Morgagni) in one of our patients could suggest an overdescent of medial thyroid anlage-derived cells in the origin of this heterotopia.

Metastases of renal cell carcinoma to the thyroid gland with synchronous benign and malignant follicular cell-derived neoplasms

Clear cell renal cell carcinoma (CCRCC) is the most common origin for metastasis in the thyroid. A 51-year-old woman was referred to our hospital for a subcarinal lesion. Ten years before, the patient had undergone a nephrectomy for CCRCC. Whole-body fluorodeoxyglucose positron emission tomography revealed elevated values in the thyroid gland, while the mediastinum was normal. An endoscopic ultrasonography-guided fine-needle aspiration biopsy of the mediastinal mass was consistent with CCRCC, and this was confirmed after resection. The thyroidectomy specimen also revealed lymphocytic thyroiditis, nodular hyperplasia, one follicular adenoma, two papillary microcarcinomas, and six foci of metastatic CCRCC involving both thyroid lobes. Curiously two of the six metastatic foci were located inside two adenomatoid nodules (tumor-in-tumor). The metastatic cells were positive for cytokeratins, CD10, epidermal growth factor receptor, and vascular endothelial growth factor receptor 2. No BRAF gene mutations were found in any of the primary and metastatic lesions. The patient was treated with sunitinib and finally died due to CCRCC distant metastases 6 years after the thyroidectomy. In CCRCC patients, a particularly prolonged survival rate may be achieved with the appropriate therapy, in contrast to the ominous prognosis typically found in patients with thyroid metastases from other origins.

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.