Higher proportion of malignancy in our group could explain a rather gradual rise in sodium as patients with SIADH secondary to underlying malignancy have a more severe and resistant hyponatraemia compared to other aetiologies of SIADH as in these patients, SIADH may not only be a result of ectopic AVP production by tumor cells but can also be a result of stimulation of AVP secretion or potentiation of AVP effects by anticancer drugs or palliative medications [16]. This evidence concerns the gene AVP and neoplasm.