PTEN and melanoma: Indeed, combined targeting of this pathway has been shown to improve the response to MAPK/ERK inhibition [56] and lack of PTEN expression, a critical negative regulator of the PI3K activity that was absent in our prototypical highly-resistant/mesenchymal-like cell line, can be found in up to 30% of melanomas, often concurrent with the BRAFV600E mutation [57].