Gene expression study by microarray technology has shown that important biological processes are differently regulated in the two tumour models: in E7 thyroid cells overexpression of cell cycle genes constitutes the most upregulated process whereas RET PTC3 thyroid cells present an upregulation of human PTC markers, of EGF-like growth factors, and extracellular remodeling genes (Burniat et al, 2008). Here, RET is linked to neoplasm.