RPN2 and osteosarcoma: Aberrant RPN2 gene overexpression has been documented to be frequently associated with multiple clinical parameters, including lymphatic metastasis, tumor grade, chemotherapy resistance and poor prognosis in a variety of tumors, including breast cancer, ovarian cancer, osteosarcoma, non-small-cell lung cancer, gastric cancer, laryngeal squamous cell carcinoma and colorectal cancer6,10,25–29, implying that RPN2 is a valid biomarker for drug response and is a potential therapeutic target.