I have UC and have researched a fair number of herbs and supplements to stave off or avoid colon cancer in my case. I have some questions -

Is he stage 4?
Does he have a bag yet?
What is his ratio of normal stools to runny?
How long does it generally take for his body to process any food he puts in it? (some days everything runs through within 20 min, 1 hr, 3 hrs.. etc)
Has the Cancer metastasized?

If it is only about alleviating pain and not clearing the cancer (i.e. if he/she is terminal and wishes to not pursue correction via herbs, etcetera), Bugleweed is an herb I understand can help with pain greatly.

This is what I would do if I had Colon cancer. I would use a live non freeze dried Probiotics (SCDEM Probiotica)TM . Pro(for)bio(life) will aid in digestion that may reduce pain. Foods rich in live active cultures like kiefer, yogurt,kombacha will also provide the tiny microbes needed to battle cancer. Print a list of the microbes in EM and ask your doctor supervision as with all medical herbs. In California ,medical cannabis is added to probiotic drinks and provides relief for the ill.

In laboratory investigations, some strains of LAB have demonstrated anti-mutagenic effects thought to be due to their ability to bind with heterocyclic amines, which are carcinogenic substances formed in cooked meat.[18] Animal studies have demonstrated that some LAB can protect against colon cancer in rodents, though human data is limited and conflicting.[19] Most human trials have found that the strains tested may exert anti-carcinogenic effects by decreasing the activity of an enzyme called β-glucuronidase[19] (which can generate carcinogens in the digestive system). Lower rates of colon cancer among higher consumers of fermented dairy products have been observed in some population studies

Yeah,

And as a preventative for Colon Cancer, simple things like soluble fiber go a looooong way. A tablespoon of Psyllium Husk in water 'll do wonders for binding and removing clogged foods in the Colon. Just have to remember to drink a lot of water when using things that are colonic / fibrous. If you bind it then leave it, you're not much better off now are ya?! Gotta flush it.