The exact mechanism by which MEK inhibitors cause hyponatremia remains unknown, although it is theorized that BRAF/MEK inhibitors lead to hyponatremia and water retention (dilutional hyponatremia) by activating aquaporin 2 (AQP2) trafficking from its intracellular compartment to the apical cell membrane of the renal tubule.9,12 In the renal collecting ducts, vasopressin regulates water permeability through AQP2. This evidence concerns the gene BRAF and Hyponatremia.