GPX4 and cancer: Before its formal definition, ferroptosis was already documented in vitro by two independent groups, who demonstrated that the erastin-mediated inhibition of the cystine/glutamate antiporter system (XC-), responsible for the Glutathione (GSH) synthesis, or the RAS-selective lethal 3 (RLS3)-mediated inactivation of the GSH peroxidase 4 (GPX4) enzyme, both were able to kill cultured cancer cells leading the oncogenic RAS mutation [12,13].