Doctors have discovered that some tumors, known as teratoma tumors, can be present in the human body from the time of birth. These tumors result from lumps of one kind of tissue forming in the wrong place. While these tumors are generally benign and harmless they are extremely frightening to think about. Having a teratoma tumor grow on the body means that a piece of tissue is out of place, kind of like having an extra mouth or nose decide it wants to form on your back. Teratoma tumors have also been known to grow hair, bones, limbs, internal organs, and eyes. In a few cases these tumors will grow their own teeth, although there are no documented cases of them taking a bite out of anything.