PTEN and neoplasm: Downstream signaling pathways following the activation of receptor tyrosine kinase include the activation of the well-known RAF/MERK/ERK and the PI3K/AKT/mTOR pathways which is controlled in part by the tumor-suppressor gene: PTEN. PTEN-deficient tumors have been reported to have enhanced sensitivity to the inhibition of mTOR pathways22.