The role of adjuvant radiotherapy in the treatment of resectable desmoid tumors

Purpose: Desmoid tumors have a high propensity for local recurrence with surgical resection. There are many reports describing good responses of desmoid tumors to irradiation, but none have clearly established the indications for adjuvant radiotherapy in treating resectable desmoid tumors. Methods and Materials: A retrospective analysis was performed on 61 patients with resectable desmoid tumor(s) who were treated at our institution from 1965 to February of 1992. Five patients had multifocal disease and are analyzed separately. Fifty-six patients had unifocal disease, of which 34 had positive surgical margins. Forty-five of the 56 patients with unifocal disease were treated with surgery alone, while 11 were treated with surgery plus adjuvant radiotherapy. Median follow-up was 6 years. Local control was measured from the last day of treatment, and all cases were reviewed by our Department of Pathology. Results: Multivariate analysis of the 56 patients with unifocal disease revealed that positive margins independently predicted for local recurrence (p ≤ 0.01). Only 3 of 22 patients with clear margins experienced a local recurrence, with a 6-year actuarial local control of 85 %. Multivariate analysis of the 34 patients with positive margins revealed that adjuvant radiotherapy independently predicted for improved local control (p = 0.01), and patients with recurrent disease had a slightly higher risk of local recurrence (p = 0.08). The 6-year actuarial local control determined by Kaplan-Meier for patients with unifocal disease and positive margins was 32% (±12%) with surgery alone, and 78% (14%) with surgery plus adjuvant radiotherapy (p = 0.02). Subgroup analysis of the patients with positive margins and recurrent disease revealed that those treated with surgery alone had a 6-year actuarial local control of 0% vs. 80% for those treated with surgery plus radiotherapy (p ≤ 0.01). Patients with positive margins and primary disease had a trend towards improved local control with adjuvant radiotherapy, but this was not statistically significant. None of the patients treated with radiotherapy developed serious complications or a secondary malignancy. Conclusions: Margin status is the most important predictor of local recurrence for patients with resectable, unifocal desmoid tumor. Adjuvant radiotherapy is indicated in the treatment of patients with positive margins following wide excision of recurrent disease. The role of adjuvant radiotherapy in patients with positive margins following resection of primary disease is controversial, and should be based on a balanced discussion of the potential morbidity from radiotherapy compared to the potential morbidity of another local recurrence. Adjuvant radiotherapy is less likely to benefit those with clear margins due to the excellent results for these patients treated with surgery alone. The local control of desmoid tumor in the adjuvant setting is excellent with total doses ranging from 50-60 Gy, with acceptable morbidity. Field sizes should be generous to prevent marginal recurrences, and large volume MRIs of patients with extremity lesions should be used to identify those patients with multifocal disease.