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Morphine May Fuel Cancer

Opioid Pain Drugs Stimulate Tumor Growth in Mice

WebMD Health News
Reviewed by Gary D. Vogin, MD

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Aug. 2, 2002 -- Morphine and other opium-based narcotics are the drugs of choice for patients with the most severe cancer pain, but intriguing early research suggests the drugs may actually cause tumors to grow. In a mouse study, morphine stimulated the formation of blood vessels that feed tumors.

It is not yet clear whether morphine and other opium-based drugs stimulate cancer growth in humans, but researcher Kalpna Gupta, PhD, says the question needs to be addressed.

"Obviously, we can't say that the same effect will be seen in humans until we do studies in humans," she tells WebMD. "What we can say is that we have seen this [tumor growth] response in mice and in cell cultures."

Gupta and colleagues at the University of Minnesota Cancer Center found that morphine doses similar to those given to cancer patients activated a chemical pathway in mice that promoted the growth of new blood vessels -- a process known as angiogenesis. Although new blood vessel growth is essential to good health, it also feeds tumors, prompting them to grow and spread throughout the body. The study, published in the Aug. 1 issue of Cancer Research, is the first to show that morphine can promote tumor growth in animals.

If confirmed in human studies, the finding could have major implications for pain control. Most, but not all, cancer patients given morphine are in the end stages of the disease. But morphine and similar drugs are also given to thousands of patients with chronic severe pain caused by non-life-threatening conditions.

"The administration of opioids is clearly not limited to those at the end of life," pain control expert Michael A. Ashburn, MD, tells WebMD. "There are tens of thousands of patients who receive morphine for severe pain caused by chronic conditions like low-back pain and arthritis. So if this link is proved, it will be extremely significant."

Ashburn says drug approval guidelines implemented by the FDA may help clarify the issue. Those guidelines require new drugs to prove that they don't cause cancer

"As an older drug, morphine does not have to meet this standard, but any new preparations containing morphine would," he says. Ashburn is medical director of the pain management center at the University of Utah and is the immediate past president of the American Pain Society.

Gupta hopes the findings will prompt the development of new treatments to manage severe pain. She says understanding the mechanism by which morphine leads to tumor growth could help researchers develop pain medications that do not promote this growth.

But Ashburn says there is nothing on the immediate horizon that could replace morphine and other opium-based drugs for the treatment of severe pain.

"We are at least a decade away from that," he says. "There are compounds in the pipeline, but they are years away. We are not even close to having medications that could replace opioids for pain control."

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