(ChemotherapyAdvisor) – New evidence suggests a link between the use of opioids to treat cancer-associated pain and disease recurrence and progression. The evidence was published in a review article entitled “The μ-Opioid Receptor in Cancer Progression: Is There a Direct Effect?” in the April 2012 issue of  Anesthesiology. Prior to the review, previous studies demonstrated the following direct effects: stimulating tumor cell proliferation and invasion and inhibiting apoptosis; indirect effects included immunosuppression. The purpose of the review was to assess the possible role of opioids in tumor progression, with a focus on the μ-opioid receptor (MOR) and its direct influence on cancer progression.

“Despite the evidence from cellular and epidemiologic animal studies, clinicians should note that there are no controlled trials in humans demonstrating a direct effect of opioids in facilitating tumor progression or of opioid antagonists in attenuating tumor progression,” the authors wrote. However, they wrote: “There is considerable evidence that chronic exposure to exogenous opioids changes the response in both brain and gut.”

The authors conclude that ongoing clinical trials in which different anesthetic and analgesic techniques are being used in cancer surgery will “provide additional information on the effect of opioids on cancer progression and recurrence and also on immune cell function. Outcome measures for the studies include local and metastatic cancer recurrence, natural killer cell and other immune cell functions, and disease-free survival.”

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