We conclude that a subset of FVPTC shares some of the molecular features of follicular tumors. Further studies are necessary to clarify the putative clinical significance (e.g. association to blood-born metastases) of PAX8-PPARgamma rearrangement, RAS mutations, and BRAF(K601E) in FVPTCs.

No abstract

The expression of simple and stratified epithelial-type cytokeratin (CK) intermediate filaments was evaluated by immunohistochemistry in a series of 41 papillary carcinomas, 10 follicular carcinomas, 2 poorly differentiated carcinomas and 34 specimens of normal thyroid parenchyma and lymphocytic thyroiditis. The aim of the study was to establish the CK profile of normal thyroid and thyroid carcinomas in order to clarify the putative application of CK immunostaining in diagnostic surgical pathology, and to evaluate whether the process of neoplastic transformation and tumour progression in the thyroid may be associated with any particular change in CK expression. Normal thyroid strongly expressed simple epithelial-type CKs 7 and 18 and, to a lesser degree, CKs 8 and 19, but did not express stratified epithelial-type CKs. The same pattern was found in lymphocytic thyroiditis, though the CK 19 immunoreactivity was stronger in these lesions than in the normal thyroid. Papillary and follicular thyroid carcinomas shared the expression of simple epithelial-type CKs 7, 8, 18 and 19. Immunoreactivity for CK 19 was frequently stronger and more widely distributed within each particular tumour in papillary than in follicular carcinomas, but it could also be detected, at least focally, in every follicular carcinoma. Strong expression of CK 19 highlighted small foci of papillary carcinoma not easily identifiable by conventional histological examination. Stratified epithelial-type CKs 5/6 and 13 were detected in a high percentage of papillary carcinomas, in contrast to their absence in follicular carcinomas and normal thyroid. The CK pattern was similar in primary and metastatic papillary carcinomas. We conclude that papillary carcinoma of the thyroid presents a distinct CK profile that may be used for diagnostic purposes.

The etiopathogenesis and the classification of oncocytic (Hürthle cell) tumors of the thyroid is reviewed with an emphasis on the role played by mitochondrial and nuclear genetic abnormalities that interfere with mitochondrial function. Oxyphilia is classified into primary or secondary and the so-called Hürthle cell carcinoma is divided into oncocytic (Hürthle cell) variants of papillary and follicular carcinoma.

Somatic mutations of the BRAF gene (BRAFV599E and BRAFK600E) were found to be closely associated with different histotypes of papillary thyroid carcinoma (PTC). The V599E mutation is highly prevalent in PTC with a papillary or mixed papillary follicular growth pattern, and the K600E mutation is apparently restricted to the follicular variant of PTC. It is usually accepted that thyroid malignancies may follow a progression path from well-differentiated to poorly differentiated (PDC) and undifferentiated (UC) carcinomas. One would expect that at least some of the less differentiated carcinomas would harbour the genetic alterations of pre-existing well-differentiated tumours. In order to find the prevalence of BRAF mutations in PDC and UC, we screened a series of 19 PDCs and 17 UCs, as well as 3 UC-derived cell lines, for both mutation types. The group of PDCs was restricted to the so-called insular and insular-like PDCs, thus excluding PTCs with solid, insular or trabecular foci of growth and PDCs displaying typical PTC nuclei. No BRAF mutations were detected in any of the 19 cases of PDC, whereas 6 of the UCs (35%) and one UC-derived cell line presented the BRAFV599E mutation. The BRAFK600E mutation was not detected in any case. We conclude that UC may progress from BRAFV599E-mutated PTC. The absence of BRAF mutations in our series of PDC supports the assumption that pure insular and insular-like PDCs are more closely related to follicular carcinoma than to PTC.