Water fasting was not recommended in cancer patients by the Worlds most experienced and foremost authority on this subject(Dr Herbert M Shelton )as having very little if any benefits.
Digestion is severely impaired in cancer cases which is why raw organic juice-nutrition (which is more easily absorbed and assimilated)would be the best policy, as practised under the Gerson protocol.
Cancer patients are usually nutrient-deficient as being one of the main causes, along with stress and metabolic toxemia.