Abstract
10039 Background: High dose (HD) chemotherapy using a busulfan-containing regimen has been proven advantageous for some high risk Ewing tumor (ET) patients. HD busulfan is not compatible with radiotherapy to central axis sites. Treosulfan is a bifunctional alkylating agent, structurally related to busulfan, that has shown to be safe even in heavily pretreated patients and patients at risk to treatment related toxicity. Methods: In vitro: In order to compare the cytotoxicity of busulfan and treosulfan, growth inhibition was tested by a modified (4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium-bromide (MTT) assay. In vivo: 11 patients with primary disseminated ET and contraindication for busulfan HD treatment and 11 patients with relapsed ET were referred to HD treosulfan (36 g/m2) and melphalan (140 mg/m2) followed by autologous stem cell rescue. Results: In vitro: Busulfan and treosulfan were cytotoxic in a time and dose dependent manner. Treosulfan was 15-fold more cytotoxic compared to busulfan. In vivo: The median age in patients with disseminated ET was 14.3 years, in relapsed ET 22.7 years. Sex distribution was equal. Response status prior to HD treosulfan was: stable disease in 4, partial response in 6, complete remission in 8, progressive disease in 1, not documented in 3 patients. Median follow up time in patients with disseminated ET was 0.91 years. All patients are alive. Four patients have relapsed within 2 years after HD treatment. Median follow up time in relapsed ET was 1.35 years. Seven patients are in remission, one patient is under treatment and two patients have died after relapse. HD was well tolerated with mucositis °3 in seven, °4 in three, stomatitis °3 in four, °4 in three , neutropenic infection °3 in three and reversible myelitis in one patient. Conclusions: Treosulfan HD treatment is a feasible therapeutic option without overt acute toxicity for patients with advanced ET. Efficacy and late effects remain to be evaluated. No significant financial relationships to disclose.
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