You probably did not know that the English name for Graviola is Soursop.  It is also called Guanabana in Spanish.  It comes from a broadleaf flowering evergreen tree native to Mexico, Central America, the Caribbean and northern South America. Soursop is also native to Sub-Saharan Africa countries that lie within the tropics. Today, it is also grown in some areas of Southeast Asia. It is in the same genus as the chirimoya and the same family as the pawpaw. In most Spanish speaking countries it is commonly known as Guanábana. In the Philippines, it is known as guyabano. In India basically in Kerala, it is known as Aathakka pazham.
The soursop is adapted to areas of high humidity and relatively warm winters, temperatures below 5 °C/41 °F will cause damage to leaves and small branches, and temperatures below 3 °C/37.4 °F can be fatal. The fruit becomes dry and is no longer good for concentrate.
Its flavor is described as a combination of strawberry and pineapple with sour citrus flavor notes contrasting with an underlying creamy flavor reminiscent of coconut or banana.
The flesh of the fruit consists of an edible white pulp and a core of indigestible black seeds. The species is the only member of the genus Annona that is suitable for processing and preservation. The sweet pulp is used to make juice as well as candies, sorbets, and ice cream flavorings.
In Mexico it is a common fruit often used for dessert as the only ingredient, or as an agua fresca beverage. Ice cream and fruit bars made of soursop are also very popular. The seeds are normally left in the preparation, and removed while consuming.
In Indonesia, dodol sirsak, a sweetmeat, is made by boiling soursop pulp in water and adding sugar until the mixture hardens. Soursop is also common ingredient for making fresh fruit juices that are sold at most of street food vendors. In Vietnam, this fruit is called mãng cầu Xiêm in the South, or quả Na in the North and is used to make juice, or eaten as is. In Cambodia, this fruit is called "Tearb Barung" literally meant "Western Custard-apple fruit." In Malaysia it is known in Malay as 'Durian Belanda' and in East Malaysia specifically the Dusun race in Sabah it is locally known as 'lampun'. Popularly it is eaten raw when it ripens. Usually the fruits are taken from the tree when they mature and left to ripen in a dark corner whereby it will be eaten when it is fully ripe i.e. it is soft when you press the fruit. It has a white flower with a very pleasing scent especially in the morning.
Nutritionally, the fruit is high in carbohydrates, particularly fructose. The fruit also contains significant amounts of vitamins C, B1 and B2. The fruit, seeds, and leaves have a number of herbal medicinal uses among indigenous peoples of regions where the plant is common.
According to some researchers the Graviola leaves are effective in treating intestinal worms and parasites.  The unripe fruit  is effective against dissentery and diarrhea and the root bark has been found effective as a fever reducer.
Graviola and Cancer. -  Lately there has been a lot of buzz on the internet about the cancer fighting properties of Graviola.  The idea that graviola is an effective cancer fighter comes from research at Purdue University's School of Pharmacy and Pharmaceutical Sciences on the active components of the tree, unique substances known as annonaceous acetogenins. The Purdue investigators found them to be potent inhibitors of cancer cells while leaving normal cells alone. They also found the compounds to be effective against drug-resistant cancer cells. But these are in-vitro results.  That is results obtained after adding the components found in graviola directly to cancer cells in a test tube.  The results were promising since the components were effective in destroting the cancer cells selectively.  But so far there are no clinical studies on humans to verify the claim that Graviola is an effective anti cancer agent in the human body. 
In Conclusion, Even if graviola is not yet proven to be effective as a treatment for human cancer, it is certainly a delicious option to add to your diet. And if this delicious fruit also may have miraculous health benefits, well... that is just icing on the cake.