According to the Paw Paw Research site:
When a person intakes a source of acetogenins, such as a capsule of standardized paw paw extract, the blood supply picks them up and delivers them throughout the body along with glucose. Although a slight amount of acetogenins may wind up in non-cancer cells, the resulting lowering of ATP production is not enough in most of these cells to cause any problems.
The huge energy requirement of the cancerous cells tends to "hog" most of the acetogenins to those cells. Furthermore, when the acetogenins start working on the "high-usage" cancer cells, the resulting drop in ATP energy production is much greater than it would be in most normal cells. Thus, if cancer cells are present in the body, the paw paw tends to affect them, while leaving the normal cells alone.In this way, paw paw helps to knock out the cancer cell's energy production mechanism without having the harmful side effects of chemo or radiation (similar to what is done with the Protocel treatment).
Unlike chemotherapy, the paw paw works to "starve" the cancer cells instead of poisoning them. Thus, the action is usually slower than chemotherapy.