Poorly differentiated (PD) thyroid carcinomas lie both morphologically and behaviorally between well-differentiated and undifferentiated (anaplastic) carcinomas. Following the original description of this entity, different diagnostic criteria have been employed, resulting in wide discrepancies and confusion among pathologists and clinicians worldwide. To compare lesions occurring in different geographic areas and the diagnostic criteria applied in those countries, we designed a study with a panel of internationally recognized thyroid pathologists to develop consensus diagnostic criteria for PD carcinomas. Eighty-three cases were collected from Europe, Japan, and the United States, and circulated among 12 thyroid pathologists. Diagnoses were made without any knowledge of the clinical parameters, which were subsequently used for survival analysis. A consensus meeting was then held in Turin, Italy, where an agreement was reached concerning the diagnostic criteria for PD carcinoma. These include (1) presence of a solid/trabecular/insular pattern of growth, (2) absence of the conventional nuclear features of papillary carcinoma, and (3) presence of at least one of the following features: convoluted nuclei; mitotic activity >or=3 x 10 HPF; and tumor necrosis. An algorithmic approach was devised for practical use in the diagnosis of this tumor.

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The histopathologic diagnosis of follicular variant of papillary thyroid carcinoma (FVPCA) can be difficult. Recent reports have suggested that this neoplasm may be frequently overdiagnosed by pathologists. We examined the observer variation in the diagnosis of FVPCA in 87 tumors by 10 experienced thyroid pathologists. The criteria that the reviewers considered most helpful for making a diagnosis of FVPCA were also assessed. A concordant diagnosis of FVPCA was made by all 10 reviewers with a cumulative frequency of 39%. In this series, 24.1% of the patients had metastatic disease (n = 21). In the cases with metastatic disease, a diagnosis of FVPCA was made by all 10 reviewers with a cumulative frequency of 66.7%, and 7 of the reviewers made a diagnosis of FVPCA with a cumulative frequency of 100%. The most important criteria used to diagnose FVPCA included the presence of cytoplasmic invaginations into the nucleus (pseudo-inclusions), abundant nuclear grooves, and ground glass nuclei. These results suggest that although the diagnosis of FVPCA is variable even among experienced thyroid pathologists, most reviewers agreed on this diagnosis for patients with metastatic disease. The use of well-defined histopathologic features should improve the consistency in diagnosing FVPCA. Since most cases with metastatic disease had obvious invasion, caution should be used in making a diagnosis of FVPCA in the absence of the major histopathologic features or clear-cut invasive growth.

A high prevalence of the BRAF(V600E) somatic mutation was recently reported in several series of papillary thyroid carcinomas (PTC). This mutation appears to be particularly prevalent in PTC with a predominantly papillary architecture. Another BRAF mutation (K601E) was detected in a follicular adenoma and in some cases of the follicular variant of PTC. The few studies on record provided controversial data on the relationship between the occurrence of BRAF mutations and clinicopathologic parameters such as gender, age and tumour staging. In an attempt to clarify such controversies we decided to enlarge our previous series to 315 tumours or tumour-like lesions diagnosed in 280 patients, including a thorough analysis of several clinicopathologic features. The BRAF(V600E) mutation was exclusively detected in PTC with a papillary or mixed follicular/papillary architecture both of the conventional type (46%) and of other histotypes, such as microcarcinoma (43%), Warthin-like PTC (75%) and oncocytic variant of PTC (55%). The BRAF(K601E) mutation was detected in four of the 54 cases of the follicular variant of PTC (7%). The mean age of patients with conventional PTC harbouring BRAF(V600E) (46.7 years) was significantly higher (P<0.0001) than that of patients with conventional PTC without BRAF(V600E) (29.5 years). The BRAF (BRAF(V600E)) mutated PTC did not exhibit signs of higher aggressiveness (size, vascular invasion, extra-thyroid extension and nodal metastasis) and were in fact less often multicentric than PTC without the mutation.

In an attempt to progress in the understanding of the relationship of mitochondrial DNA (mtDNA) alterations and thyroid tumorigenesis, we studied the mtDNA in 79 benign and malignant tumors (43 Hürthle and 36 non-Hürthle cell neoplasms) and respective normal parenchyma. The mtDNA common deletion (CD) was evaluated by semiquantitative polymerase chain reaction. Somatic point mutations and sequence variants of mtDNA were searched for in 66 tumors (59 patients) and adjacent parenchyma by direct sequencing of 70% of the mitochondrial genome (including all of the 13 OXPHOS system genes). We detected 57 somatic mutations, mostly transitions, in 34 tumors and 253 sequence variants in 59 patients. Follicular and papillary carcinomas carried a significantly higher prevalence of non-silent point mutations of complex I genes than adenomas. We also detected a significantly higher prevalence of complex I and complex IV sequence variants in the normal parenchyma adjacent to the malignant tumors. Every Hürthle cell tumor displayed a relatively high percentage (up to 16%) of mtDNA CD independently of the lesion's histotype. The percentage of deleted mtDNA molecules was significantly higher in tumors with D-loop mutations than in mtDNA stable tumors. Sequence variants of the ATPase 6 gene, one of the complex V genes thought to play a role in mtDNA maintenance and integrity in yeast, were significantly more prevalent in patients with Hürthle cell tumors than in patients with non-Hürthle cell neoplasms. We conclude that mtDNA variants and mtDNA somatic mutations of complex I and complex IV genes seem to be involved in thyroid tumorigenesis. Germline polymorphisms of the ATPase 6 gene are associated with the occurrence of mtDNA CD, the hallmark of Hürthle cell tumors.

In di use gastric carcinoma, despite common E-cadherin gene (CDH1) mutations, tumors show absence of CDH1 loss of heterozigosity (LOH) in most cases. This observation challenges the classical two-hit model of tumor suppressor gene inactivation. In order to investigate whether or not CDH1 promoter methylation may function as the second hit we analysed a series of 23 sporadic gastric carcinomas for the presence of CDH1 mutations, CDH1 promoter methylation, LOH and Ecadherin expression. CDH1 mutations were detected in nine of the 16 (56.3%) di use gastric carcinomas and in none of the seven intestinal gastric carcinomas. In di use gastric carcinomas harboring CDH1 mutations, LOH was observed in a single case. Loss of plasma membrane E-cadherin expression was consistently found in all nine cases with CDH1 mutation, suggesting that tumors inactivated the remaining CDH1 allele via a di erent mechanism. CDH1 promoter methylation was observed in nine of the 16 (56.3%) di use-type gastric carcinoma cases, including six of the nine cases (66.7%) harboring CDH1 mutations. CDH1 promoter methylation was also seen in two (28.6%) intestinal-type cases. Our results show that CDH1 promoter methylation is the second hit in more than half of the sporadic di use gastric carcinoma cases harboring CDH1 mutations. Oncogene (2001) 20, 1525 ± 1528.

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This large multicenter study demonstrates differential prognostic risks of the three major PTC variants and establishes a unique risk order of TCPTC > CPTC ≫ FVPTC, providing important clinical implications for specific variant-based management of PTC.