Methadone for 'Adenocarcinopathic' Pain Treatment

Inclusion Criteria:

* Cancer type is adenocarcinoma;
* In the physician's opinion, mechanism of pain is most likely linked to an adenocarcinoma 'in proximity to' or invading a nerve or nerve plexus (i.e., 'adenocarcinopathic' pain; ACPP);
* Experiencing poorly controlled pain (defined as pain of 4 or higher on a 10-point visual analogue scale) despite the use of non-opioid analgesics or despite the regular use of up to 60 mg morphine equivalent daily dose (MEDD);
* Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 to 2;
* Estimated prognosis of at least 3 months;
* Able to fill out questionnaires and understand procedures in English and/or French;
* Able to provide first person informed consent;
* Physician deems it appropriate to start the patient on the opioid.

Exclusion Criteria:

* Known QTc prolongation (QTc greater than 500ms, QRS less than 120ms) or known congenital QTc prolongation syndrome;
* Taking at least one medication that increases risk of Torsades de Pointes (TdP): cisapride, disopyramide, dofetilide, flecainide, procainamide, propafenone, quinidine, quinine, sotalol;
* History of opioid abuse or dependence using Edmonton Pain Classification;
* Has geographic difficulties with follow-up in person;
* Has any of the following comorbidities: documented class 3 or 4 New York Heart Association (NYHA) heart failure, myocardial infarction in the last 3 months, unstable angina, pericardial disease, oxygen dependent pulmonary diseases, Parkinson's disease, suspected or diagnosed dementia, bipolar disorder, poorly managed major depression (current or treated) or anxiety disorder;
* Taking medication known to have clinically significant interactions with the CYP450 enzyme: carbamazepine, efavirenz, phenobarbital, rifampicin, azole antifungals, antiretrovirals, grapefruit juice, clarithromycin, erythromycin;
* Diagnosed with Child-Pugh class B and/or C cirrhosis;
* Has hepatic insufficiency, defined as jaundice with irreversible hyperbilirubinemia of at least 34 micromol/L despite biliary tract stents (severity criteria in Child-Pugh-Turcotte score);
* Received radiation or any nerve block or plexus block on the same side as the pain in the past 14 days or PLANNED within the next 14 days;
* PLANNED prescription for daily co-analgesia with pregabalin, gabapentin, or dexamethasone during the next 14 days (not including dexamethasone with chemotherapy);
* Taking medication associated with major risk of serotonin syndrome (monoamine oxidase inhibitors; MAOIs): linezolid, moclobemide, rasagiline, selegiline;
* Taking medication known to be an opioid agonist, antagonist, or partial agonist: naltrexone, buprenorphine, tapentadol, tramadol;
* Other negative characteristic as per physician discretion (e.g., reduced renal function).