Expression data from benign and malignant pheochromocytomas and paragangliomas

Pheochromocytomas and paragangliomas (PPGL) are rare neuroendocrine, usually benign tumors. Currently, for these neoplasms the only reliable criterion of malignancy is the presence of metastases. The aim of the present study was to identify molecular markers that can distinguish malignant from benign PPGL. An mRNA expression array was performed on 40 benign and 11 malignant PPGL. Genes showing a significantly different expression between benign and malignant PPGL with a ratio ? 4 were selected. Differentially expressed genes were confirmed by qRT-PCR and subsequently tested in an independent validation series (4 benign and 4 malignant) by qRT-PCR. Finally, immunohistochemistry was performed for the validated genes on Tissue Micro Arrays, which included 100 PPGL (87 benign and 13 malignant). Ten genes, which were significantly differentially expressed between benign and malignant tumors (False Discovery Rates <0.05), were selected from the mRNA expression array data. Differential expression of Interleukin 13 Receptor Alpha 2 and Contactin 4 was confirmed (p<0.05) and validated by qRT-PCR. However, at the protein level, only Contactin 4 appeared to be significantly overexpressed in malignant tumors (58% in malignant versus 17% in benign; p<0.05). No difference in the immunohistochemical staining for Interleukin 13 Receptor Alpha 2 was observed between benign and malignant PPGL. Contactin 4 expression appears to be associated with malignancy in pheochromocytomas and paragangliomas, and may be predictive of malignant behavior. In totall, 40 benign pheochromocytoma/paraganglioma and 11 pheochromocytoma/paraganglioma by affymetrix mRNA expression arrays