10036 Background: Standard treatment of osteosarcoma includes cisplatin and high-dose methotrexate (HD-MTX), but both agents are associated with significant toxicity and MTX administration requires complex pharmacokinetic monitoring. In our previous OS91 trial, the combination of carboplatin and ifosfamide with doxorubicin and HD-MTX yielded outcomes comparable to those of cisplatin-based regimens with less long-term toxicity in localized osteosarcoma. METHODS Between 1999 and 2006, we conducted a multi-institutional trial (OS99) to evaluate the activity of carboplatin, ifosfamide, and doxorubicin without HD-MTX in newly-diagnosed patients with localized osteosarcoma. Treatment comprised 12 cycles of chemotherapy given every 3 weeks: 3 consecutive cycles of carboplatin (dose targeted to AUC 8 mg/ml×min on day 1) and ifosfamide (2.65 g/m2 daily for 3 days) and one cycle of doxorubicin (25 mg/m2 daily for 3 days) followed by definitive surgery (week 12) and 2 additional cycles of carboplatin/ifosfamide and 3 cycles each of ifosfamide/doxorubicin and carboplatin/doxorubicin for a total of 35 weeks. The log rank test was used to compare survival and event-free survival (EFS) distributions. RESULTS A total of 72 eligible patients were enrolled. The median age was 13.4 years and 41 (57%) were male. The most common tumor site was the femur (n = 46; 64%). The median follow-up for survivors was 4.4 years. Forty of the 66 (60.6%) evaluable patients had good histologic response (tumor necrosis > 90%) to preoperative chemotherapy. There was no difference in EFS or survival distributions between OS99 and OS91. Four-year estimates of EFS were 68.1 ± 6.7% for OS99 compared to 70.2 ± 6.6% for OS91 (p = 0.89). The 4-year OS was 82.4% ± 5.7% for OS99 compared to 74.5% ± 6.3 for OS91 (p = 0.25). CONCLUSIONS OS99 produced outcomes similar to cisplatin or HD-MTX containing regimens and offers an alternative treatment regimen especially for patients with renal compromise and institutions where pharmacokinetic monitoring of MTX is not available. No significant financial relationships to disclose.