Expression of P-Glycoprotein in High-Grade Osteosarcomas in Relation to Clinical Outcome

The resistance of tumors to multiple drugs is a major problem in cancer chemotherapy. P-glycoprotein, a transmembrane ATP-dependent efflux pump encoded by the mdr1 gene, 1 has a central role in multidrug resistance in vitro, 2 and its clinical relevance is under investigation. 3 , 4 Increased amounts of P-glycoprotein may confer multidrug resistance on cells by preventing the intracellular accumulation of a variety of cytotoxic drugs, 5 including doxorubicin, the most effective agent for the treatment of osteosarcomas. Drug resistance may represent an important prognostic factor in osteosarcoma, the most frequent primary malignant bone tumor. Although the outcome of osteosarcoma has improved considerably since . . .