The principle in natural medicine is alkaline diets/foods create an enviroment where the cancer can't grow.....while acid foods encourage cancer.....since Soda is the most alkaline substance avalible it may indeed work, to a degree.......
Did you read my post about how eating acidic/alkaline foods actually does nothing? Your stomach responds by producing less/more stomach acid, eliminating any difference in the acidity of foods. Consuming anything is not how you adjust the pH of your body. (By the way, your body naturally regulates itself to keep its pH at a certain level.)
I hate the way ignorant people slam this idea when many hundreds of people claim to have cured themselves.....I have read about wieghtlifters, accountants, firemen......people from around the world claiming this alkaline method saved them.....if nothing else it's worthy of investigation.
What you probably don't realize (most don't) is that "hundreds of people claiming" something is meaningless. Personal anecdotes are completely useless for determining the efficacy of any sort of medical/health treatment. The problem is these "hundreds of people" in reality have no idea what "cured" them. The post hoc ergo propter hoc fallacy is hard to resist.
The only way to know if something works medically is to perform a controlled, blinded study with large enough groups.