Background: Despite (neo)adjuvant chemotherapy with cisplatin, doxorubicin and methotrexate, some patients with primary osteosarcoma progress during first-line systemic treatment and have a poor prognosis. In this study, we investigated whether patients with early disease progression (EDP), are characterized by a distinctive pharmacogenetic profile.Methods and Findings: Germline DNA from 287 Dutch high-grade osteosarcoma patients was genotyped using the DMET Plus array (containing 1,936 genetic markers in 231 drug metabolism and transporter genes). Associations between genetic variants and EPD were assessed using logistic regression models. The datafile (Hurkmans_SumStat_LogReg_DMET_EarlyProgressiveDisaese_CovarMetasSexAge_GRCh37.txt) contains the results of this anaylsis.Conclusions: This study identified a novel locus in SLC7A8 to be associated with EPD in osteosarcoma.