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21-03-2012 | Genetics | Article

Evidence linking opioids with cancer growth builds



MedWire News: Opioids prescribed to relieve pain in cancer patients may stimulate the growth and spread of tumors, suggest findings from two studies published in Anesthesiology.

One study, led by Patrick Singleton of the University of Chicago, Illinois, USA, shows that opioids can enhance the malignancy of human lung cancer cells transplanted into mice. The other, led by Andrey Bortsov of the University of North Carolina at Chapel Hill, USA, demonstrates that women who possess a genetic mutation in an opioid receptor gene that makes them less sensitive to opioids have increased survival 10 years after cancer treatment.

Both studies suggest that the µ-opioid receptor critically influences tumor progression, and is likely to be of therapeutic importance.

"Epidemiologic findings suggest that the type of anesthesia we do for cancer surgery influences recurrence rate, and laboratory studies demonstrate that opioids influence tumor progression and metastasis," said Jonathan Moss (University of Chicago), co-author of an accompanying commentary, in a press release. "These studies have caused anesthesiologists to re-evaluate how best to do anesthesia and pain control for cancer patients."

Singleton and team found that cells from human lung cancers have five to 10 times the number of opioid receptors in noncancerous lug cells. When transplanted into mice, human lung cancer cells with additional copies of the opioid receptor grew at over twice the rate of cancer cells that lacked the extra receptors, and they were 20 times more likely to spread to other sites. They also found that blocking the receptors with medications, such as naloxone or methylnaltrexone, reduced tumor growth and spread.

Bortsov and colleagues looked at survival rates in 2039 breast cancer patients, and found that women with a mutation in the µ-opioid receptor gene A118G, which made them less sensitive to opioids, had significantly increased 10-year survival compared with women without the mutation. They also found that this survival difference was doubled in women who possessed two copies of the G allele as opposed to one.

"Despite the evidence from cellular and epidemiologic animal studies, clinicians should note that there are no controlled trial in humans demonstrating a direct effect of opioids in facilitating tumor progression or of opioid antagonists in attenuating tumor progression," comment Moss and co-workers.

However, they summarize that sufficient evidence exists to suggest that opioids appear to affect cancer growth, at least to an extent that merits further research.

By Chloe McIvor

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