This observational, prospective, non-interventional study will include cancer patients who need a treatment for hyponatraemia secondary to SIADH. Patients will be prescribed treatment(s) according with the clinical practice regardless of the patient participation in the study. The purpose of this NIS is to collect additional scientific and clinical information that can help in describing the characteristics of cancer patients with hyponatraemia secondary to SIADH, the current management of hyponatremia, the therapies to keep under control serum [Na+] and the guidelines for the management of this population in Italy.

Inclusion Criteria:

1. Age >= 18 years;
2. Male or female patients with a cytologically or histologically documented cancer diagnosis;
3. Moderate to severe hyponatremia: Na+ level cut off: [Na+] < 130 mmol/L;
4. Physician diagnosed Moderate to severe hyponatremia secondary to SIADH (clinical or laboratory determined as per normal routine practice of treating physician);
5. No use of diuretic agents within the week prior to evaluation;
6. Willingness to participate in the study; subjects must give their written consent to participate.

Exclusion Criteria:

1. Use of concomitant medications including demeclocycline and/or urea, by themselves or in combination with fluid restriction;
2. Subject is currently participating in a clinical trial in which the investigational medicinal product aims to treat the causes or symptoms of hyponatremia;
3. Life expectancy is lower than 3 months.

This non-interventional study will include cancer patients who need a treatment for hyponatremia secondary to SIADH in one of the hospitals participating in the study.