Phase I study of high-dose thiotepa with busulfan, etoposide and autologous stem cell support in children with disseminated solid tumors

The aim of this phase I study was to define the maximum tolerated dose (MTD) of thiotepa (TT), administered with busulfan (BU) 480 mg/m(2) and etoposide 2,400 mg/m(2), followed by autologous bone marrow transplantation (ABMT) or peripheral blood stem cell transplantation (APBSCT) support in children with solid tumors either disseminated at diagnosis or after relapse. Nineteen patients, between 2 and 16 years of age, received a high-dose chemotherapy regimen including escalating doses of TT starting from 150 mg/m(2). Subsequent dose escalation was determined by a modified Fibonacci scheme. Whenever one patient at one dosage level showed a grade III or grade IV reversible toxicity, additional patients were admitted (one by one) up to a maximum number of 6. Upon observing grade III or IV reversible toxicity in two or more systems, in 3 of the 6 patients, no further escalation was performed, and the corresponding dosage was taken as the MTD. WHO criteria were adopted to assess grade of toxicity. All patients had hematological recovery; and neutrophils and platelet engraftment were observed after median times of 12 and 29 days from stem cell infusion, respectively. The MTD of TT was determined to be 750 mg/ m(2). At this level, 3 of 6 patients experienced grade III mucositis and/or grade III gastrointestinal toxicity. No patient died of treatment-related toxicity. A dose of 750 mg/m(2) TT is the MTD when it is associated with BU 480 mg/m(2) and etoposide 2, 400 mg/m(2). This ablative regimen represents a feasible and tolerable combination for high-dose chemotherapy followed by hematopoietic stem cell rescue (HSCR). Phase II studies in children with poor-prognosis solid tumors are required to evaluate the effectiveness of this treatment.