Trastuzumab Emtasine, inhibitor of EGFR 2 (Her2) signaling, at a dose of 3.6 mg/kg every 3 weeks, can induce true hyponatremia by a Cerebral Salt Wasting Syndrome as reported in a patient with breast cancer and brain metastasis who needed repeated hospitalizations because of severe hyponatraemia (74). Here, ERBB2 is linked to Hyponatremia.