SAN DIEGO – A medication used to relieve constipation caused by pain killers resulted in fewer reports of tumor progression and may help some cancer patients live longer, suggest first-in-human results being presented at the ANESTHESIOLOGY® 2015 annual meeting
Methylnaltrexone (MNTX) eases constipation, a significant side effect of opioids, which are taken by about half of all cancer patients to relieve pain. More than 800,000 patients have taken MNTX since its approval in 2008. The new research, combining data from two randomized, placebo-controlled trials designed to test the medication’s effect on bowel function, suggests that MNTX may have a role in cancer therapy.
“Early on we suspected that MNTX might influence cancer progression as well as improve bowel function in individual palliative care patients we treated,” said Jonathan Moss, M.D., Ph.D., lead author of the study and professor of anesthesia and critical care at the University of Chicago. “After more than a decade in the lab trying to assess how MNTX affects cancer, we have the first evidence in humans that it may be associated with slowing tumor growth and improving survival.”
The study examined 229 patients with various types of advanced cancer, including lung, prostate, breast or pancreatic, who received palliative care and were being treated for opioid-induced constipation, but did not respond to conventional laxatives. Of these, 117 were given MNTX, while 112 were given a placebo.
Sixty-six patients (57 percent) who received MNTX experienced relief from constipation, while 51 patients (43 percent) did not. Those who responded to MNTX lived, on average, twice as long (118 days vs. 58 days) as those who did not respond or who took the placebo. Patients who responded to MNTX also had significantly fewer reports of tumor progression (7.6 percent) compared to those who didn’t respond (22 percent) or who took the placebo (25.4 percent), based on physician reporting of adverse events.
Researchers also analyzed the effects of MNTX on 135 patients with advanced illness other than cancer (including congestive heart failure, advanced chronic obstructive pulmonary disease and neurologic diseases) who were enrolled in the studies. There was no improvement in survival even in the patients who got relief from constipation, Dr. Moss said.
“This makes it far less likely that improved bowel function is the only explanation for our finding of improved survival in cancer patients,” said Filip Janku, M.D., co-author of the studies and assistant professor of investigational cancer therapeutics at The University of Texas MD Anderson Cancer Center, Houston. “We’re not precisely sure why MNTX was associated with fewer reports of tumor progression and longer survival in our patients – proving what causes this response is very difficult – but it could be that MNTX influences several side effects of opioids unrelated to pain relief. The findings are consistent with what was seen in the lab.”
Previous studies in mice showed that the medication slowed tumor growth and the spread of cancer.
“Whether our findings in advanced cancers can be extended to the treatment of earlier cancers, or whether the medication can help physician anesthesiologists improve care during cancer surgery – topics being studied and discussed in our specialty – will need to be tested directly,” said Dr. Moss.
*Dr. Moss is a developer of MNTX and receives royalties through the University of Chicago. He also is a paid consultant for Salix Pharmaceuticals, which markets MNTX.
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