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.
In the meantime, anesthesiologists have been re-evaluating how best to provide anesthesia and pain control in advanced cancer while minimizing the negative effects of opioids.
Dr. Eugene Viscusi, director of acute pain management at Thomas Jefferson University in Philadelphia, said the latest findings "are very significant" and fit in with emerging signs that opiates given to cancer patients during and after surgery "may play a role in tumor growth and survival."
Prior studies of breast, prostate and colon cancer, as well as melanoma, have shown fewer recurrences following surgeries that rely more heavily on regional or epidural anesthesia and less on opioids.
"So the data mounts," Viscusi said. Acute pain treatment guidelines published last month in Anesthesiology recommended routine use of epidurals and non-opioid medications such as acetaminophen, non-steroidal anti-inflammatories and ketamine, which he said produce "better pain control, fewer opioid side effects" and may produce better overall outcomes for patients.
For now and until the evidence about opioids and cancer becomes "overwhelmingly clear," Viscusi suggested that patients "seek the best pain management available but not rely primarily or totally on opioids."