Do Opioids Play Role in Cancer Growth?

iStockphoto/Thinkstock(NEW YORK) — When Dr. Jonathan Moss was developing a drug to relieve the severe constipation plaguing end-stage cancer patients taking opioid painkillers, he noticed a few of those patients lived longer than expected.

Although likely to die within a month, some “went on to live for five to six months,” Moss said.  He began to think the methylnaltrexone (Relistor) might be doing more than simply improving their ability to eat.

“I began to wonder in my mind…could it be an effect on the progression of the tumor?” he said.

Subsequent laboratory studies confirmed that Relistor inhibited tumor growth and angiogenesis — the sprouting of blood vessels that nourish tumors.

Now, almost a decade later, multiple laboratory and animal studies, are converging with some human research to suggest that opioid drugs and the body’s natural opioids may play a role in the growth and spread of cancer, according to two studies and an accompanying commentary published Tuesday in a special issue of the journal Anesthesiology.

Moss, co-author of the commentary and one of the studies, cautioned that it would be premature for cancer patients or their doctors to give up on opioids, which have a 200-year history in relieving cancer pain and post-surgical pain.

“There are no double-blind human studies showing that if you take an opioid, that you are more or less likely to have tumor progression,” said the professor of anesthesiology and critical care medicine at the University of Chicago.

Without proof provided by a “large human study,” the findings are “very interesting,” but “much too early” to change practices, said Dr. Jay Brooks, chairman of hematology/oncology at the Ochsner Clinic Foundation and Hospital in Baton Rouge, La.  He expressed concern that cancer patients might become unnecessarily worried that pain meds will make their cancers grow.

In one of the new studies, breast cancer patients survived longer if they had a gene that made them resistant to opioids (meaning they probably needed more medication to control their pain).  In the Carolina Breast Cancer Study of more than 2,039 women diagnosed between 1993 and 2001, women with invasive breast cancer who had one copy of the gene variant survived twice as long.  Survival quadrupled for those with two copies of the gene variant, according to research led by Dr. Andrey V. Bortsov, an assistant professor of anesthesiology and his colleagues at the University of North Carolina, Chapel Hill.

In the other study, led by Patrick A. Singleton, an assistant professor of medicine at the University of Chicago, researchers found that naturally occurring opioids could fuel the growth of human non-small cell lung cancer in human lung cancer cells transplanted into mice with compromised immune systems.

“What we saw was a two-fold increase in tumor growth, and even more strikingly, a 20-fold increase in metastasis,” he said in an interview.

“The two papers together are really bookends,” Moss said.  The finding that lung cancer cells have lots of so-called mu opioid receptors involved in tumor growth and spread provides “a plausible explanation for what people in North Carolina have found.  The mu opioid receptor may be very importantly involved in the progression of tumors.”

As a result, he said that receptor could become a therapeutic target for new cancer drugs.

Copyright 2012 ABC News Radio