The Role of Radiation Therapy for Symptomatic Desmoid Tumors.

Desmoid tumors have a variable clinical course that ranges from indolence or spontaneous regression to an aggressive pattern marked by local invasion. Up to half may remain stable or regress; watchful waiting is the preferred approach in the initial management of desmoid tumors. Symptomatic or progressive tumors or those that may affect adjacent critical structures require surgery, radiotherapy, or systemic therapy. Although radiotherapy effectively controls desmoid tumors in most cases, concerns regarding late toxicity exist. Definitive radiotherapy for macroscopic disease is indicated when a non-morbid complete surgical resection cannot be accomplished and provides similar control rates to surgery plus radiotherapy but avoids toxicity from combined-modality treatment (surgery and radiotherapy). Adjuvant radiotherapy can be considered for microscopically involved margins, particularly for recurrent cases or when a future recurrence may be challenging to treat. Large size, extremity site, and younger age are poor prognostic factors after radiotherapy. In the extremity, radiotherapy may have superior outcomes to surgery. Younger patients, especially children, are challenging to manage as they are at particular risk for late toxicity due to the number of potential years at risk. For patients under 20 years old, for whom a non-morbid complete resection is not possible, we recommend systemic therapy as the first line of treatment. Although the long-term efficacy of systemic therapy is unproven, this strategy allows additional time for growth and development prior to radiotherapy. In younger patients and those with axial desmoid tumors adjacent to critical organs, consideration should be given to using proton therapy as the dosimetric advantages may mitigate some of the toxicity associated with conventional radiotherapy.