Ok, that's a fair point. If we change my hypothesised experiment to be add high glucose concentration to cells and look for a cancerous tumor that is greater t

Ok, that's a fair point. If we change my hypothesised experiment to be add high glucose concentration to cells and look for a cancerous tumor that is greater than $size after $time, I think you'd find an effect (you can read about the effects of hyperglycaemia on cancer, and given that a cancer is present, it will grow more quickly in the presence of more glucose). I guess I wanted to clarify that glucose doesn't cause cancer, but I think I understand your point now, and I think we're in agreement.