Because of mutation, cancer cells have lost control of their cell cycle and will divide without the usual checks and balances. There are many of these checks and balances. Some types of cancer mutations lead to cells that have divide now signals that are permantly on. When you think about it, when in life are cells most likely to be on rather than off? Answer: during fetal development. Cells are supposed to divide when you are developing, and stop or remain under control until needed to repair tissue. As the cells that are normally supposed to be dividing are fetal, often cancer cells will assume or revert to a more immature or fetal form. In some types of cancer, we can use the fetal proteins or immature appearance as markers and thus have a way to make a diagnosis or follow treatment.