XPO1 and neoplasm: The reasons for the discrepancy between our in vitro and in vivo data on bortezomib are likely due to numerous factors, such as cross-talk with tumor-associated stromal cells [40]; however, despite this discrepancy we observed that combined proteasome and CRM1 pathway inhibition led to synergistic cytotoxicity in vitro, providing further evidence for the efficacy of dual proteasome and CRM1 pathway inhibition in treating osteosarcoma.