Benefit of Adjuvant Radiotherapy for Local Control, Distant Metastasis, and Survival Outcomes in Patients with Localized Soft Tissue Sarcoma: Comparative Effectiveness Analysis of an Observational Cohort Study

BACKGROUND: This study aimed to quantify the benefit of adjuvant radiotherapy (AXRT) for local control, distant metastasis, and long-term survival outcomes in patients with localized soft tissue sarcoma (STS). METHODS: This single-center retrospective observational study enrolled 433 STS patients who underwent surgery with curative intent. An inverse probability of treatment-weighted (IPTW) analysis was implemented to account rigorously for imbalances in prognostic variables between the adjuvant treatment groups. RESULTS: During a median follow-up period of 5.5 years, the study observed 38 local recurrences (9%), 73 occurrences of distant metastasis (17%), 63 STS-related deaths (15%), and 57 deaths from other causes (13%). As expected, patients receiving AXRT (n = 258, 60%) were more likely to have high-grade G3 tumors (p < 0.0001) than patients not receiving AXRT. A crude analysis showed that AXRT was not associated with improved recurrence-free survival [hazard ratio (HR) 1.00; 95% confidence interval (CI) 0.72–1.38; p = 0.98]. However, after IPTW, AXRT was associated with a 38% relative reduction in the risk of recurrence or death (HR 0.62; 95% CI 0.39–1.00; p = 0.05). This benefit was driven by a strong reduction in the risk of local recurrence (HR 0.42; 95% CI 0.19–0.91; p = 0.03), whereas the relative risk of distant metastasis (HR 0.69; 95% CI 0.39–1.25; p = 0.22) and overall survival (HR 0.76; 95% CI 0.44–1.30; p = 0.32) were only nonsignificantly in favor of AXRT. An exploratory analysis showed an overall survival benefit of AXRT for patients with high-grade G3 tumors (HR 0.51; 95% CI 0.33–0.78; p = 0.002). However, this finding may have been attributable to residual confounding. CONCLUSION: In this observational cohort, AXRT was associated with a 58% reduction in the relative risk of local recurrence. No consistent association between AXRT and lower risks of distant metastasis or death was observed. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1245/s10434-017-6080-3) contains supplementary material, which is available to authorized users.