Imatinib for progressive and recurrent aggressive fibromatosis (desmoid tumors): an FNCLCC/French Sarcoma Group phase II trial with a long-term follow-up

Background: Imatinib evaluated as a new treatment option in patients with recurrent or established progressive aggressive fibromatosis/desmoid tumor (AF/DT). Patients and methods: Forty patients with unresectable and progressive symptomatic AF/DT were treated with imatinib (400 mg/day for 1 year) in a Simon's optimal two-stage phase II study (P-0 = 10%, P-1 = 30%, alpha = 5%, beta = 10%). The primary end point was non-progressive at 3 months (RECIST). Results: The study population consisted of 28 women and 12 men, with a mean age of 41 (range 20-72 years). Most of the primary sites were extra-abdominal (24, 54.5%). Familial adenomatous polyposis was observed in six (15%) cases. The median follow-up was 34 months. Imatinib toxicity was similar to that previously reported in literature. Tumor assessment was validated by a central independent radiology committee for 35 patients At 3 months, one (3%) complete and three (9%) partial confirmed responses were observed. The non-progression rates at 3, 6 and 12 months were, respectively, 91%, 80% and 67%. The 2-year progression-free and overall survival rates were 55% and 95%, respectively. Two patients with mesenteric AF/DT died from progressive disease. Conclusion: Imatinib is active in the treatment of recurrent and progressive AF/DT, providing objective response and long-term stable disease in a large proportion of patients.