The Gerson diet I agree has had amazing results. Go on You tube and you can hear more about the amazing cures that continue via the work his daughter Charlotte Gerson keeps doing.. She also wrote a book with Dr Morton Walker called The Gerson Therapy. An updated version of her fathers book. It is a real must.
Also two other highly recommended books by Chris Woollams, The Rainbow Diet and Everything you need to know to beat cancer( and every kind of illness). I read this book just by chance and recommend both for not only those that are sick but also the healthy ones.Chris Woollams specialised in cancer research and his books give huge amounts of details on different illnesses, natural supplements,Alkalising the body,foods etc...
Good luck with your friend