Radiation Therapy for Aggressive Fibromatosis: The Association Between Local Control and Age.

PURPOSE: Radiation therapy (RT) is often used in the treatment of unresectable or recurrent aggressive fibromatosis (also known as desmoid tumor) typically with excellent local control. Prior reports have suggested that local control in pediatric patients with aggressive fibromatosis is poor. We aimed to report a long-term single-institution experience with the radiotherapeutic treatment of these tumors with a focus on age-dependent outcomes. METHODS AND MATERIALS: A total of 101 patients treated with RT for aggressive fibromatosis between 1975 and 2015 at a single institution were identified. A variety of demographic and treatment-related variables were abstracted from patients' medical records. Kaplan-Meier analyses were performed to investigate the relationship between these variables and local control. RESULTS: Overall survival was excellent (98% and 95% at 5 and 10 years, respectively); local control was likewise excellent (82% and 78% at 5 and 10 years, respectively). Patients aged <20 years at diagnosis had significantly worse 5-year local control than those aged >40 years at diagnosis (72% vs 97%; hazard ratio, 9.0; P = .009). Patients treated with once-daily fractionation had significantly improved 5-year local control compared with those treated with twice-daily fractionation (90% vs 73%; hazard ratio, 0.3; P = .008). Neither the presence of gross versus microscopic residual disease, initial versus recurrent presentation, number of prior surgical procedures, nor tumor size had any effect on 5-year local control. In a total of 36.6% of patients, Common Terminology Criteria for Adverse Events grade 3 or 4 toxicity developed following treatment; the frequency of toxicities was reduced in patients treated during or after 1995 (24.5%) relative to those treated prior to 1995 (51.9%, P = .02). CONCLUSIONS: RT for aggressive fibromatosis offers excellent local control and should remain the standard of care for patients with unresectable or recurrent disease. Younger patients have diminished local control relative to older patients, suggesting possible biological differences contributing to radioresistance in the pediatric and young adult population.