Soursop is another name for graviola, and there have been many reports of graviola being successful against cancer, as well as some in vitro tests indicating that compounds found in graviola can kill cancer cells. Extracts of various parts of the graviola plant have been used historically for a variety of conditions, including viruses, parasites, rheumatism, depression and arthritis.
Graviola has also been reported to sometimes cause nerve damage and side effects similar to Parkinsons. The person who devised the Sutherlandia Oleander based supplements researched graviola and determined that it would likely not be good to use in combination with oleander because it's actions counteracted those of oleander. On the other hand, my uncle continued to take graviola when he added oleander to his anti-cancer protocol and had complete success in getting rid of his cancer.
Though graviola has been successful in some instances, it has not been found to be anywhere near a miracle cure for cancers across the board and I would be very hesitant to rely on it as a sole item for fighting cancer.