As already mentioned, the aetiology of hyponatraemia in cancer is multifaceted (Figure 1). SIAD due to ectopic arginine vasopressin (AVP) secretion is the cause of hyponatraemia in many types of cancer, particularly in lung cancer. However, tumoral AVP secretion has been observed in tumours affecting nasopharynx, oropharynx, stomach, duodenum, colon, pancreas, prostate, uterus, ureter, bladder, breast and also in lymphomas, leukemias, sarcomas, brain tumours, mesotheliomas and thymomas [9], [10]