Background. Increased levels of P-glycoprotein occur in some osteosarcomas. In this study we determined the relation between P- glycoprotein status and outcome in patients with high-grade osteosarcoma. Methods. P-glycoprotein status was determined immunohistochemically in specimens of osteosarcoma of the extremities (stage II) from 92 patients who were treated with surgery and chemotherapy. The P-glycoprotein status was analyzed in relation to the length of event-free survival. Results. The presence of increased levels of P-glycoprotein in the osteosarcoma was significantly associated with a decreased probability of remaining event- free after diagnosis (P = 0.001) and the extent of tumor necrosis after preoperative chemotherapy (P=0.04) were independent predictors of clinical outcome. The risk of adverse events was increased substantially (rate ratio, 3.37; 95 percent confidence interval 1.60 to 7.10) among patients with increased levels of P-glycoprotein in tumor cells, as compared with patients who did not have increased levels of P-glycoprotein in tumor cells. Conclusions. In patients with high-grade osteosarcoma treated with surgery and chemotherapy, the presence of increased levels of P-glycoprotein in tumor cells is associated with a significantly increased risk of adverse events and is independent of the extent of necrosis after preoperative chemotherapy.
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