The cancer link to acidity is complete bollocks. A healthy body will not allow blood pH to stray outside extremely tight limits (pH 7.35-7.45). Whatever you eat, drink or dose yourself with, your lungs and kidneys work extremely quickly to restore pH to within that narrow range. "Alkali diets" etc. are a waste of time. Quackery. From Cancer Research UK (a bit simplistic and neglecting the role of the lungs):

Some myths about cancer are surprisingly persistent, despite flying in the face of basic biology. One such idea is that overly 'acidic' diets cause your blood to become 'too acidic', which can increase your risk of cancer. Their proposed answer: increase your intake of healthier 'alkaline' foods like green vegetables and fruits (including, paradoxically, lemons).

This is biological nonsense. True, cancer cells can't live in an overly alkaline environment, but neither can any of the other cells in your body.

Blood is usually slightly alkaline. This is tightly regulated by the kidneys within a very narrow and perfectly healthy range. It can't be changed for any meaningful amount of time by what you eat, and any extra acid or alkali is simply peed out in urine.
To maintain the correct balance within the body, your urine can and does change pH, depending on what you've eaten (explained in detail in this post). This can be seen by testing urine pH (acidity) after eating different foods and is the basis of the mistaken belief that diet can "make the body alkaline". But that's all you're changing, and anyone who claims otherwise simply doesn't understand how the body works. [Edited for clarity and extra links, KA 08/08/14]