A Study on How Genetics Affect Changing Opioid Pain Medications for Cancer Patients

The "switch" group involves patients who require an opioid switch. The criteria for opioid switch is if the patient experiences the following which is unable to be relieved by usual means: (1) uncontrolled pain (average pain score greater than or equal to 4/10), or (2) at least 1 uncontrolled opioid-related adverse effect (score greater than or equal to 4/10), or (3) issues with safety, such as the inability to tolerate thecurrent opioid. Reviews will be done fortnightly to determine need for opioid switching. If the patient is experiencing difficulties with their opioid in between reviews, they are able to contact the study team in between reveiws and will be assessed for suitability for opioid switching at that time. These reviews will be conducted by the palliative care trials team. When switching, patients on oxycodone will be allocated to receive morphine, whereas those on morphine will be allocated to receive oxycodone. This step may be skipped if needed for clinical safety reasons or according to clinician judgement of the safest and most effective likely treatment decision for the patient. Those requiring further opioid switch will be allocated to receiving other opioids not previously used. Participants will be required to have blood tests (for opioid pharmacokinetic and genomic analysis and biochemistry) and complete questionnaires relating to pain intensity, opioid adverse effects, mood, and quality of life. These measures will be completed at the same timepoints as the control group. Questionnaires will take up to 20 minutes to complete each time. Additionally, these measures will also be completed within 72 hours before the opioid switch and within 3-14 days after the opioid switch. There is no maximum allowed number of times that a participant may undergo opioid switch, as this will depend upon clinical need. After this 8-week active observation period, the medical record will be reveiwed for up to 52 weeks from date of enrolment to ascertain if further opioid switches occur. Opioid switching is a normal part of usual care. However, in order to fulfill the objectives of the study, this study includes only those who are on slow release oxycodone or morphine at study entry and the allocation of opioids at switching is specific to the study. The patients included in this study will form part of the registry. The registry itself is an integral part of this trial and is formed as part of the trial. Its starting date and data sources are the same as that of the trial.