Use of a sustained release opioid medication such as long-acting morphine, fentanyl patches, methadone, and buprenorphine within the last months Use of opioid medications for cancer-related pain, including codeine and dextropropoxyphene, currently or any time within weeks of Day , Cycle Use of opioid analgesics for cancer-related pain Chronic opioid use defined as daily opioid use for more than one month prior the scheduled date of surgery. Rapidly progressive symptomatic metastatic disease, as defined by the need for increased opioid analgesics within one month of registration for the treatment of pain attributed to a prostate cancer metastatic lesion; patients receiving opioids must receive approval from the principal investigator (PI) for eligibility Any concurrent opioid analgesic use (baseline opioid use must be to be eligible) Pain due to metastatic prostate cancer requiring opioid analgesics Contraindications to use of naltrexone (i.e., past history of opioid abuse or dependence or evidence of opioid use in the past days; significant hepatocellular injury as evidenced by liver enzyme levels over times normal limits). Presence of visceral metastases (e.g. lung, liver) detectable on cross-sectional imaging or bone metastases requiring the use of opioid analgesic or focal radiation treatment at the time of study entry Moderate or severe symptomatic metastatic disease, defined as a requirement for treatment with opioid analgesics for cancer-related pain within days prior to registration At Screening need for parenteral or oral opioid analgesics (eg, codeine, dextropropoxyphene) Symptomatic metastatic disease, as defined by the need for opioid analgesics for the treatment of pain attributed to a prostate cancer metastatic lesion; patients receiving opioids must receive approval from the principal investigator (PI) for eligibility Increasing use of daily doses of opioid analgesics within days prior to enrollment in the study. Currently using an opioid antagonist or partial antagonist. No past or current use of mixed opioid agonist/opioid antagonists or other opioid antagonists Patients must have used opioid medication(s) for pain at some time in the weeks prior to registration; current use of opioids (at the time of registration) and/or later during the course of the study is permitted but not required Patients who take long acting opioid medication use Chronic sustained-release opioid use for > weeks duration pre operation (op) (in the days prior to surgery) Pre-existing opioid daily use of > mg morphine sulfate equivalent for reasons not related to LAHNC. Documented history of medication abuse/misuse (e.g. unsanctioned dose escalation, broken opioid agreement etc.) Patient must be opioid-tolerant (greater than or equal to mg morphine or equivalent) and on a stable dose of oral opioids for greater than or equal to week; stable baseline opioid dosage defined as a dosage that does not fluctuate by more than % from the average dosage over one week prior to screening Patient is thought to be at risk for misuse, abuse, addiction or overdose for schedule II controlled substance, as evidenced by the following:\r\n* An Opioid Risk Tool (ORT) score of greater/less than or equal to . \r\n* A review of the California Prescription Control Monitoring Program (PDMP) Controlled Substance Utilization Review and Evaluation System (CURES) report demonstrates multiple prescribing providers and/or multiple pharmacies in the last days; the CURES report will also be used to verify opioid use, opioid dose, and current prescribing providers Chronic opioid use as defined by use of more than mg oxycodone, or equivalent, daily Known history of chronic pain disorders and/or chronic opioid use defined as > mg of oral (PO) morphine or equivalent used daily for at least days prior to enrollment Patient has a history of opioid dependence requiring rehabilitation or the use of opioid antagonists Concomitant medication as follows:\r\n* Subjects treated with gabapentin or other anticonvulsant for neuropathic pain will be required to taper the medication and discontinue for at least weeks prior to study initiation\r\n* Patients on antidepressant treatment for pain or depression (tricyclic antidepressants [TCAs], selective serotonin reuptake inhibitor [SSRI], serotoninnorepinephrine reuptake inhibitors [SNRIs] etc.) will be allowed to continue their medications provided they have been on a stable dose for at least weeks before study initiation; no dose regimen changes of antidepressants will be allowed during the study period\r\n* Patients on around-the clock opioid treatment (including tramadol) will be allowed to continue their medication provided they have been on a stable dose for at least weeks before study initiation; the maximum allowed dose of opioid will be equivalent to mg oral morphine sulfate; patients with higher doses will be required to taper down their opioid dose to maximum mg oral morphine equivalent, and continue on stable dose for weeks before enrollment in the study; pro re nata (PRN) short-acting opioids for painful CIPN treatment will not be allowed; patients receiving PRN short-acting opioids (with or without acetaminophen) for pain other than CIPN will be allowed up to daily doses, with daily recording of analgesic consumption\r\n* Treatment with nonsteroidal anti-inflammatory drug (NSAIDs) will be discontinued at least weeks before study initiation; however, low-dose aspirin (=< mg/day) will be allowed Has another painful condition requiring chronic use of opioid analgesic, gabapentin, or pregabalin History of active opioid abuse within the past months Diagnosis of cancer related pain currently treated with first line strong oral opioid analgesics such as morphine, oxycodone, oxymorphone, hydromorphone or hydrocodone Patients who are classified as being opioid tolerant by receiving a baseline MEDD of >= mg History of chronic pain and/or daily opioid use Patients on long-acting opioid medications, or scheduled (four or more times a day for seven or more days) short-acting opioid medications within the last days Chronic daily opioid requirement Opioid tolerant, taking daily doses of strong opioid pain medication in the past week On strong opioid intravenous continuous infusion morphine equivalent daily dose (MEDD) >= mg/day at the time of enrollment History of opioid abuse Cancer patients with severe pain (i.e., >= on NRS) already on opioid therapy for one week or longer, at least mg of oral morphine/day, mcg of transdermal fentanyl/hour, mg of oxycodone/day, mg oral hydromorphone/day, mg oral oxymorphone/day, or an equianalgesic dose of another opioid Participants who have used opioid-containing medications (including cough/cold medications containing codeine and/or antidiarrheals containing loperamide) in the past weeks, or who are expected to require opioid-containing medications within the duration of the treatment period Patients who have been on opioid therapy for the last weeks or more History of active opioid abuse within the past months History of active opioid abuse within the past months Chronic opioid use for over months Patient with rapidly escalating pain that require hospitalization or an intravenous opioid therapy Has had benzodiazepine, opioid or opioid like therapy initiated within hours prior to study drug administration, or is expected to receive within hours following initiation of chemotherapy except for single doses of midazolam, temazepam or triazolam