One of the reasons could be, at least in the case of FTC-133 cells, the over-activation of PI3K/ATK signaling cascade due to the presence of the inactive PTEN. The tumor suppressor gene PTEN has been shown to play an important role in the pathogenesis of variety of human cancers including, the thyroid cancer [45], [46], [47]. This evidence concerns the gene PTEN and thyroid cancer.