Association between long-term opioid use and cancer risk in patients with chronic pain: a propensity score-matched cohort study

Background: Whether long-term opioid use is an independent risk factor for cancer progression remains unclear. Therefore, we conducted a propensity score-matched population-based cohort study to compare cancer incidence between patients with chronic pain with and without opioid use. Methods: Data from January 2008 to December 2019 were obtained from the Taiwan National Health Insurance Research Database. Patients were categorised into two groups according to the presence or absence of opioid use, and matched at a 4:1 ratio. The incidence rate ratios for specific cancers were determined. Results: Propensity score-matching yielded 63 610 patients: 50 888 with opioid use (the opioid group) and 12 722 without (the non-opioid group). In a multivariate Cox regression analysis, the adjusted hazard ratio (95% confidence interval) for cancers in the opioid group compared with the non-opioid group was 2.66 (1.44–2.94; P<0.001). The incidence rate ratios (95% confidence interval) for lung, hepatocellular, colorectal, breast, prostate, head and neck, pancreatic, gastric, oesophageal, and ovarian cancers for the opioid group were 1.87 (1.41–2.43), 1.97 (1.56–2.50), 2.39 (1.87–3.03), 2.43 (1.75–3.33), 2.00 (1.35–3.03), 1.79 (1.14–2.86), 1.87 (1.13–2.12), 2.43 (1.52–3.85), 1.82 (0.92–3.70), and 2.33 (1.01–5.55), respectively. Conclusion: There was an association between long-term opioid use and development of cancer in patients with chronic pain, which should be confirmed in future studies.