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Tesi etd-04042014-183814

Thesis type
Tesi di dottorato di ricerca
The role of different molecular markers in thyroid epithelium transformation: functional studies and possible clinical implications.
Settore scientifico disciplinare
Corso di studi
relatore Prof. Bevilacqua, Generoso
tutor Dott.ssa Mazzanti, Chiara Maria
Parole chiave
  • genetic markers
  • FNA
  • c-kit
  • BRAF
  • thyroid cancer
Data inizio appello
Riassunto analitico
Background. Papillary thyroid cancer (PTC) is the most common (~90%) endocrine
malignancy. The first manifestation of the thyroid cancer is through thyroid nodules and the
most sensitive and specific diagnostic tool to detect malignancy in patients with thyroid
nodules is fine-needle aspiration biopsy (FNAB). Nevertheless, sometimes it is not efficient
enough to give a specific diagnosis leading to the so called diagnoses of indeterminate or
suspicious lesions for PTC which ranges from 20 to 30% of cases. BRAF mutational
analysis is commonly used to assess the malignancy of thyroid nodules but unfortunately it
still leaves indeterminate diagnoses. Recent studies conducted in our laboratories have
shown a significant highly decrease rather than increase in transcript of c-KIT in malignant
thyroid lesions compared to the benign ones, and it was demonstrated to be effective as a
new biomarker in the preoperative diagnosis of thyroid tumors.
Aim: The aim of the present study is mainly to investigate thoroughly the role of the c-KIT
gene in thyroid cancerogenesis, and to characterize in details the c-KIT signaling pathway
and the cause of its down-regulation in thyroid cancer. Another aim of this present study is
to identify other molecular markers in order to improve the cytological diagnosis and to
better understand the mechanisms underlying thyroid epithelium transformation.
Methods: We have collected 169 pre-operative thyroid Fine Needle Aspirate (FNA) sample.
All 169 FNA samples analyzed in this study were molecularly characterized for the presence
of the V600E BRAF mutation in exon 15. SNP analysis, methylation analysis and various
gene expression analyses were conducted in order to clarify c-Kit role in thyroid neoplastic
trasformation. Gene expression computational models (Neural Network Bayesian Classifier,
Discrimination Analysis) were built, together with ROC curves and PCA (Principal
Component Analysis) to distinguish a malignant/benign status and BRAF status. Finally a
panel of 84 Human Tyrosine Kinases gene array was amplified on 8 benign samples and 12
malignant samples.
Results: 64/103 malignant samples carried the V600E mutation while all 66 benign samples
were wild type for BRAF exon15. The results of the analysis related to c-KIT function
support our hypothesis that this receptor controls a differentiation pathway in thyrocytes.
Methylation biochemal process and 146b/222 miRNA expression account for part of the
c-KIT dowregulation.
The Bayesian Artificial Neural Network and Discriminant Analysis, made of 4 gene (KIT,
TC1, miRNA222, miRNA146b) showed a very strong predictive value (94.12% and 92.16% 7
respectively) in discriminating malignant from benign patients and it is interesting to notice
that Discriminant Analysis showed a correct classification of 100.00 % of the samples in the
malignant group, and 95.00 % by BNN. This same model defines two clearly different
genetic background related to BRAF mutational status. In the panel of 84 Human Tyrosine
Kinases gene array we found in three (malignant vs benign; V600E vs benign; WT
malignant vs benign) of the four conducted comparisons, four genes (ALK, CSK, HCK e
MSTR1) in common that had a significantly altered expression.
Conclusion: The results of this research support the idea that c-KIT is driving a thyroid cell
differentiation pathway, which results altered in thyroid neoplasm transformation. In the
same study a 4 gene model was build able to discriminate with high probability between
benign and malignant FNAs. The model is proposed to be added to the routinely BRAF
diagnostic test in order to improve FNA diagnostic accuracy solving the problems of the
nodules that otherwise would remain suspicious. Moreover the present study shows clearly
how the presence of the BRAF V600E mutation is accompanied by a unique genetic
scenario in which sets of genes specifically discriminate the mutational and wild-type status.
Several tyrosine kinase genes showed statistically significant differential expression between
malignant and benign thyroid nodules.