Updated outcome with long-term follow-up of imatinib for the treatment of progressive or recurrent aggressive fibromatosis (desmoid tumor): A FNCLCC/ French Sarcoma Group phase II trial.

10518 Background: We present updated results from a previously reported phase II trial assessing clinical efficacy of imatinib in progressive or recurrent aggressive fibromatosis (Fayette et al. ASCO 2007) Methods: Patients with aggressive fibromatosis not amenable to radiotherapy or non-mutilating surgery were eligible and received imatinib 400mg daily (increased to 800mg daily in case of progression) up to 1 year then stopped. The primary end point was non-progressive disease rate at 3 months. Independent radiological committee reviewed responses. The number of patients was calculated according to a optimal 2-stages design. RESULTS Forty patients were included between September 2004 and October 2005 in 15 centers. The median follow up is 33 months [95% CI: 32-35]. Toxicity of imatinib is similar to that previously reported. At 3 months, the nonprogression rate was 91% [95% CI: 77-96] with 1 (2%) complete and 3 (8%) partial confirmed responses observed. The non progression rates at 6, 9, and 12 months were 80%, 69% and 66% respectively. The median time to progression was 9.5 months. The 2-year progression-free survival (PFS) was 55%. No plateau was observed. The 2-year-overall survival was 95%. Two patients with mesenteric aggressive fibromatosis died from progressive disease. In multivariate analysis including clinical factors, only previous radiotherapy was associated with reduced progression free survival. None of the biological factors tested using IHC on TMA (PDGFR α, PDGFR β, β catenin, c-kit, E cadherine, MCSFR, cycline D1 and Erk) were found correlated to response, progression free or overall survival. CONCLUSIONS With a 2.8 years median follow up, this is the largest study which confirms the high efficacy of imatinib (400 mg daily) in patients presenting with aggressive fibromatosis failing local treatment and with documented evidence of progressive disease before imatinib treatment. [Table: see text].