I wrote something yesterday and lost it
As Ria says there isn't really an anti cancer diet or anything that will cure it. Only thing I'd suggest is immune boosting extras to help him keep in good health generally and able to fight things off. Brazil nuts have an ingredient that's a high immune boosting substance so giving half a shelled brazil nut once a week would be a nice extra. Or maybe a quarter twice a week as they're quite big.
Also hemp seeds contain all vitamins and minerals and healthy fats and supposed to be good for immunity. A pinch of those and a pinch of linseeds daily on a separate dish (I use a jar lid). They like them and lick them up. The linseeds make their fur lovely as well. Otherwise just general hamster food. Porridge oats are supposed to soak up free radicals (cancer causing chemicals) and hamsters love a bit of porridge. You can just make a little bit in a mug in the microwave - and give it on a teaspoon when cooled. Daily if it's not too much faff. Just a heaped teaspoon of porridge oats and a bit of water (not milk) in a mug and microwave for 10 to 30 seconds (trial and error).