May P-glycoprotein status be used to stratify high-grade osteosarcoma patients? Results from the Italian/Scandinavian Sarcoma Group 1 treatment protocol. The aim was to evaluate the clinical impact of P-glycoprotein in primary non-metastatic high-grade osteosarcoma patients, treated with neoadjuvant chemotherapy protocols. P-glycoprotein was assessed by immunohistochemistry on paraffin-embedded tissue samples collected at time of diagnosis from 94 osteosarcoma patients, treated with the Italian Sarcoma Group/Scandinavian Sarcoma Group 1 (ISG/SSG 1) protocol. P-glycoprotein-positivity at diagnosis was found in 53/94 ISG/SSG 1 cases (56%) and emerged as the single factor significantly associated with an unfavourable outcome from survival and multivariate analyses. A comparative analysis of the subgroup of 94 patients considered for P-glycoprotein evaluation and the whole series of ISG/SSG 1 patients showed that this marker retained its prognostic value also in the latter group. In osteosarcoma patients treated with doxorubicin-based chemotherapy protocols, P-glycoprotein overexpression at diagnosis is an important adverse prognostic factor for outcome. P-glycoprotein evaluation can therefore constitute the basis for stratifying, at diagnosis, osteosarcoma patients for whom alternative treatments may be considered.