He should most definitely get the cancerous tumor removed. The portal vein connects the colon & the liver, and if his cancer metasticizes, it will be the liver first. Liver cancer is very troublesome. My advice is to preserve as much of the colon as possible, but remove the tumor.
Tell your brother that many natural treatment have a long list of web testimonies, but they are mostly anecdotal (i.e. "a person", "a woman", etc.). Finding a good reference that fought and won, who will discuss the situation with you in detail is very difficult. He will not get many chances in this fight. He needs to make his decisions carefully.