Abstract

Opioids are frequently prescribed for cancer pain management, yet accumulating evidence suggests that opioid exposure may be associated with inferior outcomes in patients also undergoing treatment with immune checkpoint inhibitors (ICIs). To synthesize mechanistic and clinical evidence linking opioids to the PD-1/PD-L1 axis, the literature was searched up to 18 January 2026, with study selection and data extraction focused on (i) cancer-cell and immune-cell effects of opioid agonism or antagonism on PD-1/PD-L1 biology, and (ii) clinical studies reporting ICI outcomes (progression-free survival, overall survival, or treatment duration) with concomitant opioid exposure. Preclinical studies support multiple, non-mutually exclusive mechanisms: opioids can induce PD-L1 in tumour cells, modulate innate-inflammatory pathways (including TLR4-linked cascades), promote dysfunctional T-cell phenotypes that reduce responsiveness to PD-1 blockade, and show context- and opioid-dependent effects. Clinical cohorts and meta-analytic datasets in non-small cell lung cancer and other tumour types report associations between opioid exposure (including higher morphine-equivalent dosing) and worse ICI outcomes. The intersection of opioid signaling with PD-1/PD-L1 biology likely operates across cancer cell-intrinsic and immune cell-intrinsic pathways, providing a mechanistic rationale for prospective evaluation of opioid-sparing strategies and/or peripheral opioid antagonism as adjuncts to checkpoint blockade.

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