Is this an effective treatment for cancer? Why don't you promote it?"

Gerson therapy is not a valid or effective treatment for cancer. It should never be taken in lieu of genuine treatments like surgery, radiation therapy (radiotherapy) or chemotherapy. The Gerson regimen supposedly cures cancer through a special diet, supplements and injections of liver extracts. The diet is meant to boost the immune system and uses coffee enemas to “cleanse toxins” from the body. None of this is likely to successfully treat cancer. Some aspects, such as eating lots of fruits and vegetables, can be healthy if not taken to extremes. Others, such as coffee enemas, could be potentially harmful as well as ineffective, leading to serious illness and potentially death. 

In any case, removing toxins is a natural function of the liver and kidneys. Some antioxidant supplements can, contrary to popular belief, increase the odds of dying from cancer. To work out if something can actually treat cancer effectively, doctors run large randomised trials. This means that they compare people who receive the treatment with those who do not. No such studies have ever been done for Gerson therapy.