A transplant is the transfer of cells, tissue or an organ removed either from the patient him/herself (autotransplant) or from a donor (allotransplant or xenotransplant). The person who receives the transplant is called the recipient. Compatibility between donor and recipient is essential. The bone marrow transplant is a very delicate medical procedure used to treat some tumours, leukaemias or breast cancer following intensive chemotherapy. Bone marrow cells destroyed by the treatment or disease are then replaced by transplanted cells.