High-dose thiotepa and hematopoietic stem cell transplantation in pediatric malignant mesenchymal tumors: a phase II study.

The prognosis of metastatic malignant mesenchymal tumors (MMT) remains poor. Given the chemosensitivity of these neoplasms, a phase II study of high-dose thiotepa (HDT) was performed to evaluate the efficacy of this drug in this particular subset of pediatric tumors. Between 1986 and 1998, 18 patients, previously treated with conventional therapy for metastatic or refractory MMT, entered the study. Thiotepa was administered at a daily dose of 300 mg/m2 for 3 consecutive days. Hematopoietic stem cell rescue, consisting of bone marrow transplantation or peripheral stem cell transplantation, was performed 2 days after completion of HDT. A response exceeding 50% was observed in 6/18 patients (response rate 33%). Toxicity was severe but never led to death. HDT used at a dose of 900 mg/m2 yields measurable anti-tumor activity in previously treated patients. The next step in these particularly poor prognosis metastatic MMT will be to investigate HDT combined with other drugs, known to be efficient at high doses.