• Kirsi Santti, Annette Beule, Laura Tuomikoski, Mikko Rönty, Anna-Stina Jääskeläinen, Kauko Saarilahti, Hanna Ihalainen, Maija Tarkkanen, and Carl Blomqvist.
• Comprehensive Cancer Center, Helsinki University Hospital and University of Helsinki, PO Box 180, 00029 HUS, Helsinki, Finland. kirsi.santti@hus.fi.
• Strahlenther Onkol. 2017 Apr 1; 193 (4): 269-275.

BackgroundDesmoid tumors (aggressive fibromatosis) are rare soft tissue tumors which frequently recur after surgery. Desmoid tumors arise from musculoaponeurotic tissue in the extremities, head and neck, abdominal wall, or intra-abdominally. Our aim was to examine the outcome of radiotherapy of desmoid tumors in a single institution series.Patients And MethodsWe evaluated 41 patients with desmoid tumors treated with 49 radiotherapies between 1987 and 2012. Radiologic images for response evaluation were reassessed and responses to treatment registered according to RECIST criteria 1.1. For patients with local failures radiation dose distribution was determined in each local failure volume using image co-registration. Recurrences were classified as in-target, marginal, or out-of-target. Prognostic factors for radiotherapy treatment failure were evaluated.ResultsRadiotherapy doses varied from 20-63 Gy (median 50 Gy) with a median fraction size of 2 Gy. The objective response rate to definitive radiotherapy was 55% (12/22 patients). Median time to response was 14 months. A statistically significant dose-response relation for definitive and postoperative radiotherapy was observed both in univariate (p-value 0.002) and in multivariate analysis (p-value 0.02) adjusted for potential confounding factors. Surgery before radiotherapy or surgical margin had no significant effect on time to progression. Nine of 11 (82%) local failures were classified as marginal and two of 11 (18%) in-target. None of the recurrences occurred totally out-of-target.ConclusionsRadiotherapy is a valuable option for treating desmoid tumors. Radiotherapy dose appears to be significantly associated to local control.

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