Asian Pacific J Cancer Prev, 13,[3103][3104][3105][3106][3107]
IntroductionOsteosarcoma is the most common primary mesenchymal malignant tumor of bone tissue in human, especially in children and adolescents, which tends to metastasize early with serious outcome and is more often in the metaphyseal areas of long bone such as distal femur, proximal tibia and humerus. Long-term survival rate increases from 25% to 65% with advances in surgical techniques and chemotherapy, but this figure has no obvious improvement in many years. Investigation of its reason is many sided and the main aspect is drug-resistance during chemotherapy (Meyers et al., 2005).The tumorigenic mechanism of osteosarcoma and its respective drug-resistance are barely understood. In the past one to two decades, more and more studies suggest that some tumors are hierarchically organized, which means that these tumor cells maintains differences in their morphology, function and differentiation level (Hanahan and Weinberg, 2000;Dick, 2008). Based on the similarity shared between these tumors, many researchers have turned to a new theory, the CSCs theory, which could help people explain tumorigenesis and drug-resistance better (Dick, 2008;Visvader and Lindeman, 2008