I hope his treatment goes alright and as painlessly as possible. Here are some anti-cancer foods that everyone should eat routinely. I don't know how much help this would be to your brother, but I'm sure they would help in at least a small way and if anything it could at least be good for morale by making him feel like he is doing every little bit possible. Check it's all not contraindicated for his treatment.
Green tea-
recommended 3 cups a day. This slows cancer growth. People aren't meant to drink more than 3 cups a day because beyond this level it might slow normal growth too, so 3 cups is the recommended optimal amount to ingest daily.
Berries etc- high in antioxidants which are anti-cancer
Tomatoes, including tinned- anti-cancer, can be eaten daily
Turmeric- eaten at least twice a week. It kills cancer cells.
Red wine- anti-cancer apparently
And eating a good varied diet in general.
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Other things that might help:
Laughter, positive attitude, positive human contact, trying not to worry so perhaps keeping occupied if possible, asking your body to heal itself by visualising it healing itself and removing the cancer, praying, taking it easy, giving yourself little treats and enjoying the simple things.
Kalonji / nigella sativa / black onion seed- from an Asian shop, these have featured in Indian cooking for a very long time, and Prophet Mohammed apparently said that it could cure every disease. Often seen as little black bits in naan bread- it tastes delicious in cooking. If you eat a whole tablespoonful it makes you feel happy and chilled. I ate a tablespoon once and enjoyed it. Might be worth a try sometime as an extra little treat. On the Wikipedia it says that some studies have found it to contain anti-cancer chemicals.
Cranberry juice- helps your bladder apparently, although I don't know how
Maybe minimise exposure to carcinogenic chemicals too where possible... using natural hippy deodorant and not wearing synthetically perfumed cosmetic products in general etc.
Good luck, do all you can to get better, but be mindful not to get too goal orientated- remember to enjoy the now with him. We are all here for you too.