EGFR and Hyponatremia: Interestingly, hyponatremia was demonstrated as an independent predictive factor of non-response to therapy (likewise to poor performance status and the absence of EGFR mutations in the tumoral tissue) in patients with non-small cell lung cancer (NSCLC) treated with the EGFR inhibitor erlotinib [32], thus strengthening the hypothesis of a direct impact of low serum [Na+] on resistance to pharmacological treatment.