No abstract

Experimental evidence has shown , both in vitro and in animal models , that neoplastic growth and subsequent metastasis formation depend on the tumor's ability to induce an angiogenic switch. This requires a change in the balance of angiogenic stimulators and inhibitors. To assess the potential role of angiogenesis factors in human thyroid tumor growth and spread , we analyzed their expression by semiquantitative RT-PCR and immunohistochemistry in normal thyroid tissues , benign lesions , and different thyroid carcinomas. Compared to normal tissues , in thyroid neoplasias we observed a consistent increase in vascular endothelial growth factor (VEGF) , VEGF-C, and angiopoietin-2 and in their tyrosine kinase receptors KDR , Flt-4 , and Tek. In particular , we report the overexpression of angiopoietin-2 and VEGF in thyroid tumor progression from a prevascular to a vascular phase. In fact , we found a strong association between tumor size and high levels of VEGF and angiopoietin-2. Furthermore , our results show an increased expression of VEGF-C in lymph node invasive thyroid tumors and , on the other hand , a decrease of thrombospondin-1 , an angioinhibitory factor , in thyroid malignancies capable of hematic spread. These results suggest that , in human thyroid tumors , angiogenesis factors seem involved in neoplastic growth and aggressiveness. Moreover , our findings are in keeping with a recent hypothesis that in the presence of VEGF , angiopoietin-2 may collaborate at the front of invading vascular sprouts , serving as an initial angiogenic signal that accompanies tumor growth. (Am J Pathol 1999Pathol , 155:1967Pathol -1976

We have recently reported the activation of a new oncogene in human papillary thyroid carcinomas. This oncogene, papillary thyroid carcinoma (PTC), is a novel rearranged version of the ret tyrosine-kinase protooncogene. Thyroid neoplasms include a broad spectrum of malignant tumors, ranging from well-differentiated tumors to undifferentiated anaplastic carcinomas. To determine the frequency of ret oncogene activation, we analyzed 286 cases of human thyroid tumors of diverse histologic types. We found the presence of an activated form of the ret oncogene in 33 (19%) of 177 papillary carcinomas. By contrast, none of the other 109 thyroid tumors, which included 37 follicular, 15 anaplastic, and 18 medullary carcinomas, and 34 benign lesions, showed ret activation. (J. Clin. Invest. 1992. 89:1517-1522

Papillary thyroid carcinoma (PTC) is associated with RET and NTRK1 rearrangements and BRAF mutations. A series of 60 PTCs collected in a single center from Italian patients were histologically re-examined and subclassified as well differentiated or tall cell variant. The sample collection was analysed for the presence of all the reported PTCassociated genetic alterations through DNA or cDNA amplification, followed by automated sequencing. The analysis of exons 11 and 15 of BRAF gene revealed the T1796A (V599E) mutation in 32% of cases, and this alteration is significantly associated with PTC tall cell variant. Oncogenic rearrangements of RET and NTRK1 receptors were found in 33 and 5% of cases, respectively. No Ras mutations were detected. Overall, genetic alterations were detected in two-thirds of samples, and in no single case more than one mutational event was found simultaneously. Gene expression profiling of a subset of 31 tumors performed using cDNA microarray chips showed no strong differences in global gene expression among the different cases. However, a supervised analysis of the obtained data identified a subset of genes differentially expressed in tumors carrying BRAF mutation or RTK rearrangement.

The ret oncogene frequently has been found activated in papillary thyroid carcinomas. A previous characterization of ret activation revealed recombination of its tyrosine kinase domain and sequences derived from an uncharacterized locus (DlOS170). The mechanism leading to this recombination was identified as a paracentric inversion of the long arm of chromosome 10, inv(10)(qll.2q21), with the breakpoints occurring where ret and DlOS170 were mapped. To further characterize the activation of ret in papillary thyroid carcinomas, we have now isolated and sequenced a second type of ret oncogenic rearrangement not involving the DlOS170 locus. The nucleotide sequence indicated that the transforming activity was created by the fusion of the ret tyrosine kinase domain with part of the Rle regulatory subunit of protein kinase A (PKA). This is the first example of an oncogenic activity involving a PKA gene. PKA is the main intracellular cyclic AMP receptor, and its RIax subunit gene is located on chromosome 17q. Rlo-ret transcripts encode two isoforms of the chimeric protein (p76 and p81), which display constitutive tyrosine phosphorylation as well as a tyrosine kinase enzymatic activity. Under nonreducing conditions, both isoforms are found in a dimeric configuration because of both homo-and heterodimer formation. Thus, the in vivo activation of ret in human papillary thyroid carcinomas is provided by the fusion of its tyrosine kinase domain with different genes and can be mediated by different mechanisms of gene rearrangement.