Can morphine accelerate the spread of cancer?

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Research presented last week at a major cancer research conference suggests that morphine, which is regularly prescribed to cancer patients to treat pain, may actually spur cancer growth. For the past seven years, the notion that opiates might stimulate cancer growth has slowly been gaining attention in the medical research community, beginning with anecdotal evidence that patients treated with alternative pain maintenance regimes—or those given opiate blockers during treatment—tended to survive longer than patients treated with the routine pain relief medications. And two studies presented in Boston last week at a meeting of the American Association for Cancer Research, the National Cancer Institute, and the European Organization for Research and Treatment of Cancer, demonstrate that in lab cultures and live mice, blocking opiate exposure to cancer cells limited both growth and spread of the disease.

Of course, these preliminary findings need to be further substantiated before any clinical changes will be implemented, but if the research is confirmed, researchers say that the opiate blocker used in these studies may present a simple and effective way for patients to experience the pain relieving benefits of morphine, without the risk of accelerating the spread of cancer. In the two studies, which examined different types of lung cancer cells, researchers confirmed that the opiate blocker methylnaltrexone (MNTX) limited both the proliferation and migration of cancer cells. Additionally, in the animal study, researchers found that mice without a particular opiate receptor did not develop tumors when injected with cancerous cells, compared with normal mice with the receptor. They also found that normal mice (with opiate receptors) treated with MNTX had 90% less cancer growth than normal mice given opiates but no blocker.

This current research not only offers some evidence to support earlier medical observations regarding opiate-spurred cancer growth, but may even suggest an accessible solution to the problem. If the findings are replicated, researchers say, MNTX could easily be incorporated into pain relief treatments. MNTX was approved by the Food and Drug Administration in the U.S. in 2008, but was first introduced in the 1980s by Leon Goldberg, the late pharmacologist for the University of Chicago, who modified an existing opiate blocker to counter opiate-induced side effects, including constipation, while preserving its ability to relieve pain.