Besides the contoversy over the use of embryotic stem cells, there are many cons to using human embryotic stem cells. Embryonic carcinoma (EC) cell lines are derived from the undifferentiated compartment of murine (rodent) and human germ cell tumors. Being cancer-derived and usually aneuploid, EC cells are not suitable for clinical application because they can sometimes cause cancer. Since the use of embryotic stem cells is very controversial, embryotic stem cells are extremely hard to obtain and extremely expensive. Embryotic stem cell theropy would be unrealistically expensive for a client. Also, the progress in directing and characterizing the in vitro differentiation of murine ES cells is significantly more advanced than for human ES cells. Although embryonic stem cells have the broadest differentiation potential, their use for cellular therapeutics is excluded for several reasons: the uncontrollable development of teratomas in a syngeneic transplantation model, imprinting-related developmental abnormalities, and ethical issues. There is a risk with all transplants that the allogeneic ES cell-derived implants could be rejected by the host.