To summarize before I go on: We are alkaline to begin with, so the idea that an alkaline environment is bad for diseases is simply wrong. Making the body more alkaline will kill the patient. Lots of other things can kill cancer or other diseases, but they will all kill the patient, too, like acidity, or heat, or deprivation of oxygen, or glucose, etc.
I have a feeling, and forgive me if I am jumping to conclusions here but I have a feeling that this question is about one of the latest trends in marketing : "alkaline" diets.
I described earlier that our blood pH is very (and I emphasized VERY) tightly regulated. One part of that is that there is almost nothing you can eat or drink that will affect your pH. Certainly not the "alkaline water" that is being sold everywhere now. Think about this. It's true that pure water is at a pH of 7.0, which is neutral. But does that really matter? We eat fruits, most of which are acidic. Are we saying that fruits are bad? Or what about meat? It has a pH, like most tissues, around the same as our body, so why drink alkaline water, when you can just eat meat? Does the idea that the pH of our food affects our blood pH even make sense? No, it does not.
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And now let me take a more general perspective on this question. It is in a broad category of questions: I read somewhere [or heard, or saw in an advertisement] that doing X will cure diseases. So why don't doctors do X?
The answer to that is: Because X does not work in the real world, and X is being sold to people, hoping that the customer is too ignorant to know better.
