Effect of opioids on cancer survival in patients with chronic pain: a propensity score-matched population-based cohort study

Background: The impact of opioid analgesic use before cancer diagnosis on survival in patients with chronic pain is unclear. Therefore, we designed a propensity score-matched population-based cohort study to compare overall and cancer-related survival of patients with chronic pain who received long-term opioid analgesic treatment with that of those who did not receive such treatment. Methods: We included patients with chronic pain and categorised them into the following two groups according to their analgesic use: patients with cancer and chronic pain who were prescribed ≥180 defined daily doses of opioid analgesics per year >3 months before cancer diagnosis comprised the case group, and those who were prescribed <28 defined daily doses of opioid analgesics per year before cancer diagnosis comprised the control group. Patients in both groups were matched at a ratio of 1:5. The primary outcome was overall long-term survival. Results: The matching process yielded a final cohort of 1716 patients (286 and 1430 in the case and control groups, respectively) who were eligible for further analysis. The adjusted hazard ratio for overall survival in patients receiving long-term opioids was 3.53 (95% confidence interval: 3.03–4.11; P<0.001). Conclusions: Long-term opioid analgesic use before cancer diagnosis might be associated with poor overall survival in patients with chronic pain compared with such patients who did not receive long-term opioid analgesics.