FGF2 and neuroblastoma: Highly tumorigenic NB CSC-candidate cells were successfully enriched by non-serum/bFGF/EGF medium because as few as 10 passaged tumor sphere cells from aggressive NB injected orthotopically into severe combined immune-deficient/Beige mice formed large NB tumors that metastasized to the liver, spleen, contralateral adrenal gland and kidney, and lungs [14].