Effects of opioids on immunologic parameters that are relevant to anti-tumour immune potential in patients with cancer: a systematic literature review

Background: The immune system has a central role in controlling cancer, and factors that influence protective antitumour immunity could therefore have a significant impact on the course of malignant disease. Opioids are essential for the management of cancer pain, and preclinical studies indicate that opioids have the potential to influence these tumour immune surveillance mechanisms. The aim of this systematic literature review is to evaluate the clinical effects of opioids on the immune system of patients with cancer. Methods: A systematic search of Ovid MEDLINE (PubMed) and Embase, Cochrane database and Web of Knowledge for clinical studies, which evaluated the effects of opioids on the immune system in patients with cancer, was performed. Results: Five human studies, which have assessed the effects of opioids on the immune system in patients with cancer, were identified. Although all of these evaluated the effect of morphine on immunologic end points in patients with cancer, none measured the clinical effects. Conclusions: Evidence from preclinical, healthy volunteer and surgical models suggests that different opioids variably influence protective anti-tumour immunity; however, actual data derived from cancer populations are inconclusive and definitive recommendations cannot be made. Appropriately designed and powered studies assessing clinical outcomes of opioid use in people with cancer are therefore required to inform oncologists and others involved in cancer care about the rational use of opioids in this patient group.