Certainly wont cure it, but it can help with treatment side effects. There's a drug they sometimes give to chemo patients to help with the side effects called Marinol. The active ingredient is a synthetic form of THC.
Though, I wouldn't recommend eating it for a first timer, it's much more difficult to control dosage. Say he doesn't like the feeling of being high, well, he's already eaten a bunch of it so it's too late now. I personally don't like cooking my weed for this reason, I usually miss my target high level and end up only a little high or way too stoned.
In all though it's a good way to deal with any pain or treatment side effects he may have, but it wont get rid of the cancer.
I am fairly sure though that if he tried smoking a little it wouldn't do him harm... unless maybe coughing hurts?
