The association between different opioid doses and the survival of advanced cancer patients receiving palliative care
© The Author(s). 2016
Received: 13 June 2016
Accepted: 15 November 2016
Published: 21 November 2016
Concerns that opioids may hasten death can be a cause of the physicians’ reluctance to prescribe opioids, leading to inadequate symptom palliation. Our aim was to find if there was an association between different opioid doses and the survival of the cancer patients that participated in our palliative care program.
A retrospective study was conducted at Ramathibodi Hospital, Bangkok between January 2013 and December 2015. All of the cancer patients that were referred to palliative care teams by their primary physicians were included in the study. The study data included the patients’ demographics, disease status, comorbidities, functional status, type of services, cancer treatments, date of consultation, and the date of the patient’s death or last follow-up. The information concerning opioid use was collected by reviewing the medical records and this was converted to an oral morphine equivalent (OME), following a standard ratio. The time-varying covariate in the Cox regression analysis was applied in order to determine the association between different doses of opioids and patient survival.
A total of 317 cancer patients were included in the study. The median (IQR) of the OME among our patients was 6.43 mg/day (0.53, 27.36). The univariate Cox regression analysis did not show any association between different opioid doses (OME ≤ 30 mg/day and > 30 mg/day) and the patients’ survival (p = 0.52). The PPS levels (p < 0.01), palliative care clinic visits (HR 0.32, 95%CI 0.24–0.43), home visits (HR 0.75, 95%CI 0.57–0.99), chemotherapy (HR 0.32, 95%CI 0.22–0.46), and radiotherapy (HR 0.53, 95%CI 0.36–0.78) were identified as factors that increased the probability of survival.
Our study has demonstrated that different opioid doses in advanced cancer patients are not associated with shortened survival period.
Opioids have been recommended by the WHO for the first-line treatment of moderate to severe cancer pain and the use of strong opioids for dyspnea management has been considered an efficacious and safe treatment [1, 2]. Despite the availability of the drugs, inadequate pain management has been found among cancer patients [3, 4]. One of the most frequent causes of undertreatment is misconceptions about opioids [5–8].
There are still ongoing fears surrounding the use of opioid analgesics among patients, families, and health care professionals. A qualitative study revealed that many patients and families believed that opioids should be only used in terminal cases and at the end of life, and that opioid use may be associated with premature death . Another study that attempted to identify the barriers to cancer pain management in Taiwan demonstrated that informed family caregivers of advanced cancer patients had concerns about reporting pain and administering opioids, particularly as they related to disease progression and possible side effects . Additionally, previous studies on the physician’s attitude toward prescribing opioids for dyspnea showed that the most frequently-reported barriers regarding the prescription of opioids were the resistance of the patient, fear of potential adverse effects, and fear of respiratory depression [6, 8]. A study in the Netherlands on the perceptions of physicians concerning opioid use and the survival of the patient showed that physicians more often took hastening death into account when they gave higher doses of opioids when the patient experienced more severe symptoms and with female patients .
With regard to the concerns of the potential adverse events related to opioid use, the current evidence regarding the effect of opioids on the patient’s survival is still conflicting. Some studies have indicated a potential association of increased survival with higher doses of opioids or increases in opioid doses in the last days of life [10–14]. Some studies on the other hand did not show any significant survival difference between those that were taking opioids and those that were not [15–17]. In other studies, higher opioid doses or increasing doses of opioids were reported to be associated with shorter survival, although some of these did not examine the effect of opioids on survival as a primary endpoint [18–20]. Several retrospective studies have suggested that opioid use might promote tumor progression and as a result negatively impact the survival of patients with advanced cancer [21–23]. Additionally, opioid doses have been seen to be correlated with low testosterone, and hypogonadal males were seen to have a shorter survival compared with those that were eugonadal . The analysis from a large chemotherapy RCT showed that opioid use was independently associated with shorter survival . Regarding two recent systematic reviews on the association between systemic opioid analgesia and survival among cancer patients [26, 27], the results showed that there was no clear association between opioid doses or increasing doses of opioids and survival; other studies showed that opioids might be associated with decreased survival, while others suggested that opioids improved survival or had no effect.
The Department of Family Medicine at Ramathibodi Hospital, Mahidol University, had a project on the development of palliative care for people in the Bangkok metropolitan area beginning in 2010. The project is aimed at the integration of palliative care services into mainstream medicine in Thailand by providing a variety of services, including inpatient consultation, a palliative care clinic, telephone consultation, as well as providing home-based palliative care. Around 700 patients and their families participated in this project from January 2010 to December 2015. Among these patients, 90% were diagnosed with cancer. The aim of this study was to find if there was an association between different opioid doses and the survival of the cancer patients that participated in our palliative care program.
This retrospective cohort study was conducted in the Department of Family Medicine at Ramathibodi Hospital, Bangkok, Thailand, between January 2013 and December 2015. All of the patients with a cancer diagnosis that were referred to palliative care teams by their primary physicians, e.g., oncologists, surgeons or internists (both inpatient and outpatient consultation), were included into the study. The time from the first palliative consultation to the study endpoints was estimated for each subject. The endpoints of patient follow up were death, referral to other catchment areas, or the end of the study period. The study’s participants were censored, if they were referred to other catchment areas or were still alive at the end of study period (December 31th, 2015). The primary outcome was all-cause mortality.
The study data were collected using a standardized data record form. The data set was comprised of the patient’s demographics (age, gender, marital status), disease status (primary tumor sites, presence of metastases), comorbidities assessed by using the Charlson Comorbidity Index(CCI) , functional status assessed using the Palliative Performance Scale Adult Suandok, which was translated into Thai from the Palliative Performance Scale (PPSv2) , types of palliative care service, concurrent cancer treatments, date of patient consultation with the palliative care service, and the date of death or the patient’s last follow-up.
Types of Opioids (Route)
10 mg (IV), 15 mg (SC)
Pethidine hydrochloride (IV)
100 mg (IV)
Codeine phosphate tablet (Oral)
Fentanyl citrate (IV)
Methadone and Tramadol
Morphine dose equivalence not being reliably established
The average daily opioid use of each patient during those specific periods was calculated by using the sum of the OME in that period divided by the number of days. For example, the average daily OME in the first week = Sum of OME in the first weeks divided by 7. Based on the previous data from our palliative program, which showed that most patients survived 2–3 months after the palliative consultation, we decided to calculate the average daily OME on a weekly basis for the first three months and then on a monthly basis until the study endpoints.
The opioid doses were categorized into 2 groups: 1) ≤ 30 mg/day and 2) > 30 mg/day, based upon the recommended total daily starting dose for opioids in palliative care [31, 32]. The opioid dosages varied according to time, depending on the symptom severity and clinical conditions of the patients. Therefore, they were considered in the model as a time-dependent variable. The survival probability among the two categories of opioid doses was estimated using Kaplan–Meier curves and they were compared using the Log-rank test. The univariate Cox proportional hazards regression model was applied to assess the association between risk of death and different opioid doses, as well as other possible prognostic factors (i.e., age, sex, marital status, types of cancer, services, and concurrent cancer treatments, metastases, and baseline PPS and CCI). The multivariate Cox proportional hazards regression was applied to determine the independent association between those variables and risk of death. Only the factors that had a P-value less than 0.15 from the univariate model were considered in the multivariate Cox proportional hazards model.
All of the analyses were performed using STATA version 14. A P-value less than 0.05 was considered to be a statistically-significant level.
Characteristics of the patients (N = 317)
Age (median; range)
63 years (19–95)
Types of malignancies
• Gastrointestinal cancer
• Primary lung cancer
• Head and neck cancer
• Genitourinary cancer
• Breast cancer
No evidence of metastases at initial consultation
PPS level (%)a
• ≤ 30
• ≥ 70
Charlson comorbidity index
• ≤ 3
• > 3
Types of service
• Hospital admission
• Palliative care clinic visit
• Home visit
Concurrent cancer treatments
Types of opioidsb
• Morphine sulfate (Oral)
• Morphine sulfate (Intravenous)
• Morphine sulfate (Subcutaneous)
• Fentanyl TTS 12 mcg/h
• Fentanyl TTS 25 mcg/h
• Fentanyl TTS 50 mcg/h
• Fentanyl citrate (Intravenous)
• Pethidine hydrochloride (Intravenous)
• Codeine phosphate (Oral)
Patient status at the last follow-up
The univariate Cox regression analysis revealed that the patients with PPS levels of 40 to 60% and greater than 70% had a higher chance of survival than patients with a PPS level of 30% and below 30%, with a hazard ratio of 0.27 (95%CI 0.20–0.38) and 0.11 (95%CI 0.07–0.16) respectively. Moreover, a palliative care clinic visit (HR 0.32, 95%CI 0.24–0.43), a home visit (HR 0.75, 95%CI 0.57–0.99), chemotherapy (HR 0.32, 95%CI 0.22–0.46), and radiotherapy (HR 0.53, 95%CI 0.36–0.78) were identified as factors that increased the probability of survival. On the other hand, the patients that needed hospital admission had a higher probability of dying (HR 2.03, 95%CI 1.54–2.67).
Univariate Cox regression analysis of factors associated with survival
Number of deaths (%)
• Age < 60
• Age ≥ 60
Type of malignancy
• Head and neck cancer
• Breast cancer
• Primary lung cancer
• Gastrointestinal cancer
• Genitourinary cancer
Evidence of metastases at consultation
• ≤ 30
• ≥ 70
Type of service
• No home visit
• Home visit
• No palliative care clinic visit
• Palliative care clinic visit
• No hospital admission
• Having hospital admission
• No chemotherapy
• Receiving chemotherapy
• No radiotherapy
• Receiving radiotherapy
• No surgery
• Receiving surgery
Charlson comorbidity index (CCI)
• ≤ 3
• > 3
Oral morphine equivalent (mg/day)
• ≤ 30 mg/day
• > 30 mg/day
Cox regression analysis of the association between different morphine doses and the survival among palliative care patients that received morphine only (N = 118)
Number of deathsa (%)
Hazard ratio (95%CI)
Adjusted Hazard ratiob (95%CI)
• ≤ 30 mg/day
• > 30 mg/day
4.13 (1.83, 9.31)
Concerns that opioids may hasten death can be a cause of physicians’ reluctance to prescribe or increase the dosage of opioids in palliative care settings, and could contribute to insufficient symptom palliation in the latest stage of cancer. The present study looked at the survival of cancer patients that received palliative care in various settings, e.g., outpatient, inpatient, and home care. We did not find any association between different opioid doses and the survival of the cancer patients in our palliative care program. This finding agrees with clinical experience and the findings of previous studies of palliative care populations [11–14, 16, 17, 35].
On the other hand, when we performed the post hoc subgroup analysis to find out if there was any association between different morphine doses and the survival among patients that received morphine only, we surprisingly found that a higher dose of morphine was associated with shorter survival period. This finding is consistent with the results from previous studies that showed the effects of morphine on cancer progression/recurrence and survival with some specific types of cancers, although the effects of morphine on these outcomes are still poorly understood [21, 25, 36, 37]. It is also worth mentioning that these effects have been explored in preclinical models using morphine as the archetypical opioid . Nevertheless, the number of patients with OME > 30 mg/day in this subgroup analysis was very low and all died. This could be one limitation of the analysis and we believe that further, well-designed study is required to clarify if there is an association between classes of opioids and the survival of cancer patients. Moreover, there may be other potential confounding factors, such as the patients’ final symptom levels, that were not recorded in our study. Thus those patients needing a higher dose of morphine might have worse symptoms or at least need a higher dose to control them. A more advanced disease might mean increased levels of pain, necessitating higher doses of morphine. Therefore, it is too early to come to a conclusion concerning these effects of morphine in clinical practice.
The patients participating in our study had a median survival of 33 days, ranging from 1 to 995 days. This follow-up period was longer than that discussed in previous literature, where the follow-ups were generally short, over days or only a short number of weeks . To the best of our knowledge, ours is the first study to analyze opioid use from the time of palliative consultation until the patient’s death by using the time-dependent covariate analysis in the Cox regression model, which represented the variation of actual opioid exposure better than measuring only the increased dose or the opioid dose used during the last days of life, as performed by other studies [14, 15, 18, 39, 40].
We also found that the higher Palliative Performance Scale, chemotherapy, and radiotherapy were among the factors strongly correlated with longer survival of the patients, which was consistent with previous reports [41–44]. Moreover, the patients that visited the palliative care clinic or had a home visit tended to survive longer, and the patients that needed hospital admission lived a shorter length of time in our study. This could be explained by the fact that only patients with good clinical or functional status survived long enough to receive those interventions, and those with complex conditions that needed hospital admission had a greater chance of dying earlier.
There are some limitations of our study worth mentioning. Since our study was a retrospective cohort study, the sample was not randomly determined. Other variables or residual confounders could have affected the differences between groups. It is worth mentioning that the doses of methadone and tramadol were not included in the analysis. Although, few patients received those opioids, this might have affected the results of the study to some extent. Most of the patients in our study were exposed to relatively low doses of opioids and this may have led to a “floor effect” where we may not have seen the significant difference in the survival among patients with different opioid doses in our study. Additionally, a patient’s survival is influenced by many complex factors that may not be measurable. For example, depression was identified as a factor associated with mortality among advanced cancer patients in a longitudinal study . The effect of opioids on survival may be from better pain relief, which may interact with the patient’s psychological distress or depression. Moreover, most of our cancer patients survived for a few months after the palliative consultation. Therefore, the chronic effect (months to years) of opioids on survival was not adequately illustrated in this study. Further, there are wide differences in published opioid equianalgesic ratios and critical individual factors, such as gender differences, organ dysfunction, bidirectional differences of equivalence with certain opioids, drug interactions, and interindividual differences in pharmacokinetics and pharmacodynamics, which may impact equianalgesic doses . Therefore, the calculated equianalgesic dose to oral morphine in this study may represent only the estimated opioid exposure and not the real-life exposure for each individual patient.
Our study has demonstrated that the use of opioids of different doses in the palliative care population is not associated with shortened survival time. Based on our available data, we recommend that opioids be continued for pain control in patients with advanced cancer, as the ultimate goal of palliative care is to provide patients with the best quality of life during the trajectory of the illness. Nevertheless, future clinical research is required to clarify if there are any associations between different classes of opioids and the survival of cancer patients.
Oral morphine equivalent
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Availability of data and materials
The de-identified study data are available to all interested researchers upon request to the corresponding author.
AS prepared the proposal, performed the data collection and analysis, and reviewed the manuscript. KN participated in drafting the proposal and the design of the study, data analysis, and writing the manuscript. TA participated in drafting the design of the study, performing the data analysis and reviewing the manuscript. All of the authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Consent for publication
All authors have given consent for this article to be published.
Ethics approval and consent to participate
This project has been reviewed and approved by the Committee on Human Rights Related to Research Involving Human Subjects, Faculty of Medicine, Ramathibodi Hospital, Mahidol University. Reference number: MURA2015/645. Written informed consent to participate was provided by all participants.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
- WHO’s cancer pain ladder for adults: World Health Organization. Available from: http://www.who.int/cancer/palliative/painladder/en/. Accessed 1 June 2016.
- Lopez-Saca JM, Centeno C. Opioids prescription for symptoms relief and the impact on respiratory function: updated evidence. Curr Opin Support Palliat Care. 2014;8(4):383–90. doi:10.1097/SPC.0000000000000098.View ArticlePubMedGoogle Scholar
- Reis-Pina P, Lawlor PG, Barbosa A. Cancer-related pain management and the optimal use of opioids. Acta Med Port. 2015;28(3):376–81.View ArticlePubMedGoogle Scholar
- Teno JM, Clarridge BR, Casey V, Welch LC, Wetle T, Shield R, et al. Family perspectives on end-of-life care at the last place of care. JAMA. 2004;291(1):88–93.View ArticlePubMedGoogle Scholar
- Garcia-Toyos N, Escudero-Carretero MJ, Sanz-Amores R, Guerra-De Hoyos JA, Melchor-Rodriguez JM, Tamayo-Velazquez MI. Preferences of caregivers and patients regarding opioid analgesic use in terminal care. Pain Med. 2014;15(4):577–87. doi:10.1111/pme.12376.View ArticlePubMedGoogle Scholar
- Janssen DJ, de Hosson SM, bij de Vaate E, Mooren KJ, Baas AA. Attitudes toward opioids for refractory dyspnea in COPD among Dutch chest physicians. Chron Respir Dis. 2015;12(2):85–92. doi:10.1177/1479972315571926.View ArticlePubMedGoogle Scholar
- Lin CC, Wang P, Lai YL, Lin CL, Tsai SL, Chen TT. Identifying attitudinal barriers to family management of cancer pain in palliative care in Taiwan. Palliat Med. 2000;14(6):463–70.View ArticlePubMedGoogle Scholar
- Rocker G, Young J, Donahue M, Farquhar M, Simpson C. Perspectives of patients, family caregivers and physicians about the use of opioids for refractory dyspnea in advanced chronic obstructive pulmonary disease. CMAJ. 2012;184(9):E497–504. doi:10.1503/cmaj.111758.View ArticlePubMedPubMed CentralGoogle Scholar
- Rurup ML, Borgsteede SD, van der Heide A, van der Maas PJ, Onwuteaka-Philipsen BD. Trends in the use of opioids at the end of life and the expected effects on hastening death. J Pain Symptom Manage. 2009;37(2):144–55. doi:10.1016/j.jpainsymman.2008.02.010.EpubAug9.View ArticlePubMedGoogle Scholar
- Bercovitch M, Adunsky A. Patterns of high-dose morphine use in a home-care hospice service: should we be afraid of it? Cancer. 2004;101(6):1473–7.View ArticlePubMedGoogle Scholar
- Bengoechea I, Gutierrez SG, Vrotsou K, Onaindia MJ, Lopez JM. Opioid use at the end of life and survival in a Hospital at Home unit. J Palliat Med. 2010;13(9):1079–83. doi:10.89/jpm.2010.0031.View ArticlePubMedGoogle Scholar
- Azoulay D, Hammerman-Rozenberg R, Cialic R, Ein Mor E, Jacobs JM, Stessman J. Increasing opioid therapy and survival in a hospice. J Am Geriatr Soc. 2008;56(2):360–1. doi:10.1111/j.532-5415.2007.01536.x.View ArticlePubMedGoogle Scholar
- Azoulay D, Jacobs JM, Cialic R, Mor EE, Stessman J. Opioids, survival, and advanced cancer in the hospice setting. J Am Med Dir Assoc. 2011;12(2):129–34. doi:10.1016/j.jamda.2010.07.012.EpubOct16.View ArticlePubMedGoogle Scholar
- Good PD, Ravenscroft PJ, Cavenagh J. Effects of opioids and sedatives on survival in an Australian inpatient palliative care population. Intern Med J. 2005;35(9):512–7.View ArticlePubMedGoogle Scholar
- Radha Krishna LK, Poulose JV, Tan BS, Goh C. Opioid use amongst cancer patients at the end of life. Ann Acad Med Singapore. 2010;39(10):790–7.PubMedGoogle Scholar
- Alsirafy SA, Galal KM, Abou-Elela EN, Ibrahim NY, Farag DE, Hammad AM. The use of opioids at the end-of-life and the survival of Egyptian palliative care patients with advanced cancer. Ann Palliat Med. 2013;2(4):173–7. doi:10.3978/j.issn.2224-5820.2013.10.02.PubMedGoogle Scholar
- Minami S, Fujimoto K, Ogata Y, Yamamoto S, Komuta K. Opioids have no negative effect on the survival time of patients with advanced lung cancer in an acute care hospital. Support Care Cancer. 2015;23(8):2245–54. doi:10.1007/s00520-014-2592-6.View ArticlePubMedGoogle Scholar
- Portenoy RK, Sibirceva U, Smout R, Horn S, Connor S, Blum RH, et al. Opioid use and survival at the end of life: a survey of a hospice population. J Pain Symptom Manage. 2006;32(6):532–40.View ArticlePubMedGoogle Scholar
- Lin YL, Lin IC, Liou JC. Symptom patterns of patients with head and neck cancer in a palliative care unit. J Palliat Med. 2011;14(5):556–9. doi:10.1089/jpm.2010.0461.View ArticlePubMedGoogle Scholar
- van Hooft JE, Dijkgraaf MG, Timmer R, Siersema PD, Fockens P. Independent predictors of survival in patients with incurable malignant gastric outlet obstruction: a multicenter prospective observational study. Scand J Gastroenterol. 2010;45(10):1217–22. doi:10.3109/00365521.2010.487916.View ArticlePubMedGoogle Scholar
- Singleton PA, Moss J, Karp DD, Atkins JT, Janku F. The mu opioid receptor: a new target for cancer therapy? Cancer. 2015;121(16):2681–8. doi:10.1002/cncr.29460.View ArticlePubMedGoogle Scholar
- Zylla DM. Impact of opioid use on survival in patients with newly diagnosed stage IV non-hematologic malignancies. 2015 Palliative Care in Oncology Symposium; 2015.
- Nguyen J, Luk K, Vang D, Soto W, Vincent L, Robiner S, et al. Morphine stimulates cancer progression and mast cell activation and impairs survival in transgenic mice with breast cancer. Br J Anaesth. 2014;113 Suppl 1:i4–13. doi:10.1093/bja/aeu090.View ArticlePubMedPubMed CentralGoogle Scholar
- Skipworth RJ, Moses AG, Sangster K, Sturgeon CM, Voss AC, Fallon MT, et al. Interaction of gonadal status with systemic inflammation and opioid use in determining nutritional status and prognosis in advanced pancreatic cancer. Support Care Cancer. 2011;19(3):391–401. doi:10.1007/s00520-010-0832-y.View ArticlePubMedGoogle Scholar
- Halabi S, Lin CY, Kelly WK, Fizazi KS, Moul JW, Kaplan EB, et al. Updated prognostic model for predicting overall survival in first-line chemotherapy for patients with metastatic castration-resistant prostate cancer. J Clin Oncol. 2014;32(7):671–7. doi:10.1200/JCO.2013.52.3696.View ArticlePubMedPubMed CentralGoogle Scholar
- Boland JW, Ziegler L, Boland EG, McDermid K, Bennett MI. Is regular systemic opioid analgesia associated with shorter survival in adult patients with cancer? A systematic literature review. Pain. 2015;156(11):2152–63. doi:10.1097/j.pain.0000000000000306.View ArticlePubMedGoogle Scholar
- Lopez-Saca JM, Guzman JL, Centeno C. A systematic review of the influence of opioids on advanced cancer patient survival. Curr Opin Support Palliat Care. 2013;7(4):424–30. doi:10.1097/SPC.0b013e328365763a.View ArticlePubMedGoogle Scholar
- Charlson ME, Pompei P, Ales KL, MacKenzie CR. A new method of classifying prognostic comorbidity in longitudinal studies: development and validation. J Chronic Dis. 1987;40(5):373–83.View ArticlePubMedGoogle Scholar
- Chewaskulyong B, Sapinun L, Downing GM, Intaratat P, Lesperance M, Leautrakul S, et al. Reliability and validity of the Thai translation (Thai PPS Adult Suandok) of the Palliative Performance Scale (PPSv2). Palliat Med. 2012;26(8):1034–41. doi:10.177/0269216311424633.View ArticlePubMedGoogle Scholar
- Mercadante S, Caraceni A. Conversion ratios for opioid switching in the treatment of cancer pain: a systematic review. Palliat Med. 2011;25(5):504–15. doi:10.1177/0269216311406577.View ArticlePubMedGoogle Scholar
- Klepstad P, Kaasa S, Borchgrevink PC. Starting step III opioids for moderate to severe pain in cancer patients: dose titration: a systematic review. Palliat Med. 2011;25(5):424–30. doi:10.1177/0269216310386280.View ArticlePubMedGoogle Scholar
- NICE. Palliative care for adults: strong opioids for pain relief UK2016 [updated August 2016]. Available from: https://www.nice.org.uk/guidance/cg140/resources. Accessed 1 Sept 2016.
- Mercadante S, Bruera E. Opioid switching in cancer pain: From the beginning to nowadays. Crit Rev Oncol Hematol. 2016;99:241–8. doi:10.1016/j.critrevonc.2015.12.011.View ArticlePubMedGoogle Scholar
- Naito T, Kawakami J. Interindividual variation of pharmacokinetic disposition of and clinical responses to opioid analgesics in cancer pain patients. Yakugaku Zasshi. 2015;135(5):709–15. doi:10.1248/yakushi.14-00234-4.View ArticlePubMedGoogle Scholar
- Thorns A, Sykes N. Opioid use in last week of life and implications for end-of-life decision-making. Lancet. 2000;356(9227):398–9.View ArticlePubMedGoogle Scholar
- Lennon FE, Mirzapoiazova T, Mambetsariev B, Poroyko VA, Salgia R, Moss J, et al. The Mu opioid receptor promotes opioid and growth factor-induced proliferation, migration and Epithelial Mesenchymal Transition (EMT) in human lung cancer. PLoS One. 2014;9(3):e91577. doi:10.1371/journal.pone.0091577. eCollection 2014.View ArticlePubMedPubMed CentralGoogle Scholar
- Niu DG, Peng F, Zhang W, Guan Z, Zhao HD, Li JL, et al. Morphine promotes cancer stem cell properties, contributing to chemoresistance in breast cancer. Oncotarget. 2015;6(6):3963–76.View ArticlePubMedPubMed CentralGoogle Scholar
- Sacerdote P, Manfredi B, Mantegazza P, Panerai AE. Antinociceptive and immunosuppressive effects of opiate drugs: a structure-related activity study. Br J Pharmacol. 1997;121(4):834–40.View ArticlePubMedPubMed CentralGoogle Scholar
- Morita T, Tsunoda J, Inoue S, Chihara S. Effects of high dose opioids and sedatives on survival in terminally ill cancer patients. J Pain Symptom Manage. 2001;21(4):282–9.View ArticlePubMedGoogle Scholar
- Sykes N, Thorns A. The use of opioids and sedatives at the end of life. Lancet Oncol. 2003;4(5):312–8.View ArticlePubMedGoogle Scholar
- Kim AS, Youn CH, Ko HJ, Kim HM. The survival time of terminal cancer patients: prediction based on clinical parameters and simple prognostic scores. J Palliat Care. 2014;30(1):24–31.PubMedGoogle Scholar
- Kristensen A, Vagnildhaug OM, Gronberg BH, Kaasa S, Laird B, Solheim TS. Does chemotherapy improve health-related quality of life in advanced pancreatic cancer? A systematic review. Crit Rev Oncol Hematol. 2016;15(16):30008–7.Google Scholar
- Mei AH, Jin WL, Hwang MK, Meng YC, Seng LC, Yaw WH. Value of the Palliative Performance Scale in the prognostication of advanced cancer patients in a tertiary care setting. J Palliat Med. 2013;16(8):887–93. doi:10.1089/jpm.2012.0556.View ArticlePubMedGoogle Scholar
- Myers J, Kim A, Flanagan J, Selby D. Palliative performance scale and survival among outpatients with advanced cancer. Support Care Cancer. 2015;23(4):913–8. doi:10.1007/s00520-014-2440-8.View ArticlePubMedGoogle Scholar
- Lloyd-Williams M, Payne S, Reeve J, Dona RK. Thoughts of self-harm and depression as prognostic factors in palliative care patients. J Affect Disord. 2014;166:324–9. doi:10.1016/j.jad.2014.05.029.View ArticlePubMedGoogle Scholar
- Conversion Between Opioid Analgesics: A practical guide from the University of Alberta Multidisciplinary Pain Centre Faculty of Medicine & Dentistry, University of Alberta. Available from: https://www.ualberta.ca/medicine/institutes-centres-groups/multidisciplinary-pain-centre/for-healthcareprofessionals/opioid-conversion-guide. Accessed 1 June 2016.
- Canadian Guideline for Safe and Effective Use of Opioids for Chronic Non-Cancer Pain: Michael G. DeGroote National Pain Centre 2010. Available from: http://nationalpaincentre.mcmaster.ca/opioid/index.html. Accessed 1 June 2016.
- Choosing and Changing Opioids: Scottish Palliative Care Guidelines; 2014. Available from: http://www.palliativecareguidelines.scot.nhs.uk/guidelines/pain/choosing-and-changing-opioids.aspx. Accessed 1 June 2016.
- Breitbart W, Chandler S, Eagel B, Ellison N, Enck RE, Lefkowitz M, et al. An alternative algorithm for dosing transdermal fentanyl for cancer-related pain. Oncology (Williston Park). 2000;14(5):695–705. discussion.Google Scholar
- National List of Essential Medicines: Food and Drug Administration Thailand, Ministry of Public Health. Available from: http://drug.fda.moph.go.th:81/nlem.in.th/medicine/essential/list/73.