ObjectiveThis study aimed to evaluate the role of postoperative radiotherapy (RT) in dermatofibrosarcoma protuberans (DFSP) and identify the prognostic factors influencing the disease-free survival (DFS).MethodsA total of 184 patients with DFSP were analyzed from 2000 to 2016. The regression model was used to examine the prognostic factors for DFS. Baseline covariates were balanced using a propensity score model. The role of RT was assessed by comparing the DFS of the surgery + RT group with that of the surgery group.ResultsThe median follow-up was 58months (range, 6-203months). The 5-year DFS rate was 89.8%. The univariate analysis showed that age50years, presence of fibrosarcoma, margins <2cm, and tumor size 5cm were associated with worse DFS (P=0.002, P<0.001, P=0.030, and P=0.032, respectively). The multivariate Cox regression model revealed that age, margin width, lesion number, and histological subtype independently affected DFS. The Ki-67 expression was related to age and histological subtype. Patients with Ki-6717% showed a worse DFS than those with Ki-67<17% (35.8% vs 87.8%, P=0.002). In the matched cohort, DFS was significantly higher in the S+RT group than in the S group (5-year DFS, 88.1% vs 56.2%, P=0.044).ConclusionsAge, margin width, lesion number, and histological subtype were independent risk factors for DFS in patients with DFSP. The high expression of Ki-67 could predict a poor prognosis. Postoperative RT could improve DFS for patients with DFSP.