Introduction. Osteosarcoma relapse has a poor prognosis, with less than 25% 
survival at 5 years. We describe the experience of the French Society of 
Paediatric Oncology (SFCE) with high dose (HD) thiotepa and autologous stem cell 
transplantation (ASCT) in 45 children with relapsed osteosarcoma. Patients and 
Methods. Between 1992 and 2004, 53 patients received HD thiotepa (900 mg/m(2)) 
followed by ASCT in 6 centres. Eight patients were excluded from analysis, and 
we retrospectively reviewed the clinical radiological and anatomopathological 
patterns of the 45 remaining patients. Results. Sixteen girls and 29 boys 
(median age, 15.9 years) received HD thiotepa after initial progression of 
metastatic disease (2), first relapse (26), and second or third relapse (17). We 
report 12 radiological partial responses and 9 of 31 histological complete 
responses. Thirty-two patients experienced further relapses, and 13 continued in 
complete remission after surgical resection of the residual disease. Three-year 
overall survival was 40%, and 3-year progression-free survival was 24%. Delay of 
relapse (+/- 2 years from diagnosis) was a prognostic factor (P = 0.011). No 
acute toxic serious adverse event occurred. Conclusion. The use of HD thiotepa 
and ASCT is feasible in patients with relapsed osteosarcoma. A randomized study 
for recurrent osteosarcoma between standard salvage chemotherapy and high dose 
thiotepa with stem cell rescue is ongoing.