Opioids and cancer recurrence

Purpose of review With the majority of deaths from cancer because of their metastases, strategies to reduce this from occurring are at the forefront of treatment. It has been hypothesized that morphine may result in an increase in cancer metastases, following many in-vitro and animal studies, but the evidence from human retrospective data is inconclusive. This article will explore the possible mechanisms by which opioids can impact on the natural history of the cancer cell and whether they are likely to be harmful in individuals with cancer. Recent findings Although there have been trials demonstrating benefits with regional anaesthesia techniques (opioid sparing) in the surgical population, it is not clear whether the source of the benefit arises directly from the avoidance of opioids or an added benefit afforded by regional anaesthesia. Research has shown that in particular cancer cell types, morphine may actually be beneficial and that the mu-opioid receptor (MOR) plays a role in cancer disease. With the crystal structure of the MOR having recently been elucidated, this may offer new opportunities for treatments aimed at reducing cancer metastasis. Summary The role opioids play in the development of cancer metastasis and recurrence is far from clear and appears to differ depending on the cancer cell type in question. Prospective randomized controlled trials are currently underway in humans to help clarify the situation further and there results are awaited with anticipation. The negative impact of pain on the immune system is well documented and it appears that appropriate analgesia is paramount in minimizing this. Opioids still constitute a central role in the management of moderate-to-severe cancer pain.