BRAF mutational analysis in papillary carcinomas with mixed follicular and papillary growth patterns

Heterogeneity of Thyroid Cancer

There are 5 main histological types of thyroid cancers (TCs): papillary, follicular (also known as differentiated), poorly differentiated, anaplastic (the most aggressive form), and medullary TC, and only the latter arises from thyroid C cells. These different forms of TCs show significant variability, both among and within tumours. This great variation is particularly notable among the first 4 types, which all originate from thyroid follicular cells. Importantly, this heterogeneity is not limited to histopathological diversity only but is also manifested as variation in several genetic and/or epigenetic alterations, the numbers of interactions between the tumour and surrounding microenvironment, and interpatient differences, for example. All these factors contribute to the great complexity in the development of a tumour from cancer cells. In the present review, we summarise the knowledge accumulated about the heterogeneity of TCs. Further research in this direction should help to gain a better understanding of the underlying mechanisms contributing to the development and diversity of TCs, paving the way toward more effective treatment strategies.

The Value of HBME-1 and Claudin-1 Expression Profile in the Distinction of BRAF-Like and RAS-Like Phenotypes in Papillary Thyroid Carcinoma

This study compared the expression profile of HBME-1 and claudin-1 in 90 papillary thyroid carcinomas (PTCs) with respect to the tumor architecture and invasive growth as reflected in 46 BRAF-like, 31 non-invasive RAS, and 13 invasive RAS-like phenotypes. Individual tumors were given an expression score (max 300) by multiplying the percent positive tumor cells by the intensity score (range 0-3). The higher expression of HBME-1 and claudin-1 distinguished BRAF-like phenotype from RAS-like phenotype. The same correlation was also retained for both markers when comparing BRAF-like phenotype with non-invasive and invasive RAS-like phenotypes. The expression scores and positivity rates for both markers did not yield any statistical difference among BRAF-like PTCs. Except the higher positivity rate of HBME-1, invasive RAS-like tumors were not statistically different than their non-invasive counterparts with respect to the positivity rate of claudin-1 and the expression scores of both markers. A central lymph node dissection or selective lymph node sampling was available in 20 specimens. The absence of claudin-1 expression has not been a feature of lymph node metastasis in this series. Despite the limited number of nodal sampling, BRAF-like phenotype and claudin-1 positivity status have been considered the best determinants of positive predictive value and negative predictive value in the prediction of lymph node metastasis among variables, respectively. Adoption of the simplified architectural classification approach to PTCs showed distinct biomarker expression profile in this series; however, immunohistochemistry for HBME-1 and claudin-1 does not seem to be useful in the distinction of invasive RAS-like PTCs from their non-invasive counterparts. Given the overlapping molecular signatures within the RAS-like phenotype, further studies with additional biomarkers are still needed to identify distinct protein expression signatures of non-invasive RAS-like phenotype as this diagnostic category still remains a surgical diagnosis at this time.

Gene expression profile of human thyroid cancer in relation to its mutational status

This review describes the gene expression profile changes associated with the presence of different mutations that contribute to thyroid cell carcinogenesis. The results are discussed in the context of thyroid cancer biology and of the implications for disease prognosis, while the diagnostic aspect has been omitted. For papillary thyroid cancer (PTC), the most characteristic gene expression profile is associated with the presence of BRAF mutation. BRAF-associated PTC differ profoundly from RET/PTC or RAS-associated cancers. Simultaneously, they retain many characteristic gene expression features common for all PTCs, induced by the alternative mutations activating MAPK pathway. Although the difference between papillary and follicular thyroid cancer (FTC) is significant at the gene expression profile level, surprisingly, the RAS-related signature of FTC is not well specified. PAX8/peroxisome proliferator-activated receptor γ (PPARγ) rearrangements, which occur in FTC as an alternative to the RAS mutation, are associated with specific changes in gene expression. Furthermore, the difference between well-differentiated thyroid cancers and poorly differentiated and anaplastic thyroid cancers is mainly a reflection of tumor degree of differentiation and may not be attributed to the presence of characteristic mutations.

Encapsulated papillary oncocytic neoplasms of the thyroid: morphologic, immunohistochemical, and molecular analysis of 18 cases

Encapsulated papillary oncocytic neoplasms (EPONs) of the thyroid are rare tumors, whose relationship to other thyroid tumors has not been thoroughly elucidated. Earlier, they have been regarded as variants of papillary thyroid carcinoma (PTC), hyperplastic lesions, and follicular neoplasms. Eighteen EPONs were retrieved from our surgical pathology files and reviewed for defining morphologic features. Cases having the typical nuclear features of PTC were excluded. Immunohistochemistry (IHC) for CK19, HBME1, and CD56 was carried out. Microdissection, polymerase chain reaction, and sequencing of exon 15 of the BRAF gene were completed. Cases were evaluated for rearranged in transformation/papillary thyroid carcinoma RET/PTC rearrangement by fluorescent in situ hybridization (FISH). The majority of the tumors exhibited a distinctive histologic appearance. They were composed of true papillae lined by a single layer of predominantly cuboidal cells with oncocytic cytoplasm; hobnailing was typically prominent. Three tumors showed taller cells with uniformly apical nuclei and no hobnailing. Ten of 18 cases showed vascular and/or capsular invasion; hence, if the diagnostic criteria used to evaluate follicular neoplasms are applied, more than half of the tumors would be considered minimally invasive carcinomas. No cases were immunoreactive with antibodies to HBME1, whereas only 1 of 13 was immunoreactive for CK19. Six of 7 interpretable cases were immunoreactive for CD56. No BRAF point mutations or RET/PTC rearrangements were identified in the examined cases. All patients were alive at the time of last follow-up and no locally recurrent disease had been reported; however, 1 case was remarkable for a lymph node metastasis. Our results confirm that EPONs are histologically, immunohistochemically, and molecularly distinct from papillary thyroid carcinoma and seem to be most related to follicular neoplasms.