Conversion From Parenteral to Oral Methadone.

Inclusion Criteria:

* diagnosis of advanced disease of any type of malignancy;
* \>18 years old at the time of inclusion;
* for inclusion in the screening phase, the patient is a candidate to pass parenteral methadone to oral methadone (MTD) following to the physician criteria.
* for inclusion in the assessment phase should follow: presence of cancer pain controlled with no significant toxicity with MTD VP for 48h. Be considered controlled pain and absence of significant toxicity due to MTD, as the definitions given in the general protocol;

  e) signing the informed consent form.

Exclusion Criteria:

1. impairment cognitive status that interferes with the assessment;
2. diagnosis of psychiatric disorders at the time of recruitment that alters the ability to evaluate;
3. presence of side effects due to chemotherapy and / or radiotherapy prior to the change of route of administration, taking into account the following two criteria:

   * For patients on a protocol of successive cycles of chemotherapy (no change in chemotherapy regimen), having presented side effects due to chemotherapy in the 15 days prior to the change of route of administration as clinically and following the recommendations of the 2011 4th ed Oncomecum of the Spanish Society of Medical Oncology and deemed that may interfere with the assessment of the primary endpoint.
   * For patients starting a new protocol of chemotherapy or radiotherapy, have submitted side effects due to such treatment in the 28 days prior to the change of route of administration based on clinical judgment and following the recommendations of the Oncomecum 2011 4th ed. of the Spanish Society of Medical Oncology and deemed that may interfere with the assessment of the primary endpoint.
4. invasive anesthesic techniques have been made during the 3 days before changing to oral parenteral;
5. patients at agony.