This 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).

A 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.

The median follow-up was 58 months (range, 6-203 months). The 5-year DFS rate was 89.8%. The univariate analysis showed that age ≥ 50 years, presence of fibrosarcoma, margins < 2 cm, and tumor size ≥5 cm 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-67 ≥ 17% 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).

Age, 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.