This is not new but it does not seem to be well known. First, just
what is "Naltrexone"? Go to:
http://www.nida.nih.gov/PODAT/PODATindex.html and click on:
"Narcotic Antagonist Treatment Using Naltrexone" and you"ll
get the paste below:

Narcotic Antagonist Treatment Using Naltrexone for opiate addicts
usually is conducted in outpatient settings although initiation of
the medication often begins after medical detoxification in a
residential setting. Naltrexone is a long-acting synthetic opiate
antagonist with few side effects that is taken orally either daily or
three times a week for a sustained period of time. Individuals must
be medically detoxified and opiate-free for several days before
naltrexone can be taken to prevent precipitating an opiate abstinence
syndrome. When used this way, all the effects of self-administered
opiates, including euphoria, are completely blocked. The theory
behind this treatment is that the repeated lack of the desired opiate
effects, as well as the perceived futility of using the opiate, will
gradually over time result in breaking the habit of opiate addiction.
Naltrexone itself has no subjective effects or potential for abuse
and is not addicting. Patient noncompliance is a common problem.
Therefore, a favorable treatment outcome requires that there also be
a positive therapeutic relationship, effective counseling or therapy,
and careful monitoring of medication compliance.

Well, you can see that patients who are on morphine pain medication
could not take naltrexone

Go to:
http://www.digitalnaturopath.com/treat/T74481.html click on "colon
cancer" and get to:
http://www.digitalnaturopath.com/cond/C387945.html

For lots more refs, put "naltrexone colon cancer" into www.google.com/

Best
Ed