Stem cell therapy, like any other treatment, carries with it the possibility that the patient's immune system will reject the cells that are employed in the treatment. The enormous promise that stem cells have is that they are able to divide an infinite number of times and differentiate into a wide variety of cell types. Despite these remarkable capabilities, stem cells paradoxically have the capacity to give rise to malignant tumours. Due to the existence of these possible dangers, both patients and medical professionals must proceed with extreme caution.