A contemporary analysis of radiotherapy effect in surgically treated retroperitoneal sarcoma

Background and purpose: Contemporary data regarding the benefit of radiotherapy in surgically treated retroperitoneal sarcoma are scarce. The aim of the study was to evaluate the effect of radiotherapy on cancer specific mortality in surgically treated patients according to tumor size, histological subtype and grade. Material and methods: Within Surveillance, Epidemiology, and End Results database (2004–2014), we identified 1226 patients with non-metastatic retroperitoneal sarcoma. Univariable and multivariable logistic regression models tested for predictors of radiotherapy delivery. Univariable and multivariable Cox regression models tested the effect of radiotherapy on cancer specific mortality in the overall population. Subgroup analyses explored the result of tumor grade and tumor size on radiotherapy effect. All analyses were repeated after adjustment according to inverse probability of treatment. Additionally, all analyses were subjected to 1000 bootstrap resamples for internal validation. Results: Radiotherapy was delivered in 372 patients (30.3%). In univariable and multivariable logistic regression models high grade (OR: 1.46, CI:1.12–1.90; p = 0.006), and leiomyosarcoma histologic subtype (OR: 2.14, CI: 1.55–2.95; p < 0.001) predicted radiotherapy delivery. In the overall population multivariable Cox regression models showed lower cancer specific mortality (HR: 0.73, CI: 0.55–0.96; p = 0.025) with radiotherapy. In subgroup analyses multivariable Cox regression models showed radiotherapy benefit predominantly in high grade, large tumor size retroperitoneal sarcomas (HR 0.51: C.I.: 0.30–0.86; p = 0.02). Conclusions: In this retrospective report, delivery of radiotherapy was associated with lower cancer specific mortality in high grade, large tumor size retroperitoneal sarcoma patients. Our findings are predominantly representative of liposarcomas and leiomyosarcomas that accounted for 90% of study population. Further study is needed to evaluate the role of radiotherapy in retroperitoneal sarcoma patients.