Maybe you could ease your brother around to a more academic (and less emotional) stance by trying to encourage him to get more information and make decisions based on that. I would ask the doctor what the evidence is for metastasis, and how they know it's not a primary tumor. Then I'd ask for clues as to why they believe its a tumor and not a vascular thing or something else. Then, of course, what other tests will provide more definitive information. I'm sure he feels like he's been thrown under a bus ... maybe it would help him to feel like he's fighting back without giving in. It sounds like he might be scared and hiding it behind defiance.