You might want to research Dr. William Donald Kelley on that. He says cancer is the changing of an ectopic germ cell into an ectopic trophoblast cell. In pregnancy, the trophoblast cells metastize (as cancer does) to form the placenta. At about the seventh week, the baby's pancreas develops and its enzymes, along with the mother's pancreatic enzymes, stop the growth of the placental trophoblastic tissue. In cancer, the growth of tissue happens at the wrong place and the wrong time, which according to Kelley is caused by an inbalance of sex hormones and a deficiency of pancreatic enzymes.