You would like to think that you could trust a doctor, but that is not always true. In fact, there is one example where the doctor was guilty of stealing something from the body of a man from Seattle, which just comes across as being seriously unethical.
The man was admitted to UCLA and during tests it was discovered that he had some pretty unique blood cells. These blood cells proved to be rather good at helping to fight infection so the doctors that were treating him decided that they had to do something about all of this.
It led to them stealing cells from his body without telling him or letting him know in any way that he had something pretty unique about him. They then proceeded to develop a form of medicine from those cells and at no point did they pay the man anything or get his consent at any stage. So, it seems that nothing in your body is sacred, not even your cells.