APEX1 and osteosarcoma: Most studies to determine whether APE1 can be used as a predictive marker showed that high-level expression or cytoplasmic staining was associated with poor outcome and resistance to chemoradiotherapy in patients with lung cancer, breast cancer, head and neck cancer, osteosarcomas, germ cell tumors and hepatocellular carcinomas [7], [9]–[11], [24].