Histologic Response Following Pre-Operative Radiotherapy for Soft Tissue Sarcoma (STS) in a French Reference Center and Review

Abstract

Background and Purpose: Limb sparing surgery and radiotherapy is the main treatment of patients harboring soft tissue sarcoma of the extremity. There is limited data regarding the prognostic impact of histologic response after pre-operative radiotherapy. Patients and Methods: Between 2010 and 2018, 123 patients were treated with a pre-operative radiotherapy for soft tissue sarcoma at Leon Berard Centre (Lyon, France) and were retrospectively reviewed. All patients received a dose of 50 Gy in 25 fractions. The histologic response has been analysed by considering the following factors: necrosis ≥ 90%, percentage of viable tumor cells ≤ 10% and fibrosis ≥ 10%. Overall survival (OS), local recurrence-free survival (LRFS), distant recurrence-free survival (DRFS) and event-free survival (EFS) were evaluated. Results: Median follow up was 33.2 months (range 2.3-128.1 months). Local recurrence occurred in 9 patients (7.5%) and 40 patients (33%) presented a distant recurrence. The 2 and 5-year OS was 84% and 63%. Histologic response factors (necrosis ≥ 90%, viable tumor cells ≤ 10% and fibrosis ≥ 10%) were not predictive in DRFS and EFS. In multivariate analysis, grade was the only significant prognostic factor for EFS P=0.0087. Among the 14 patients with ≤ 10% viable cells after irradiation 13 presented a metastatic evolution within 6 months. Conclusion: This study showed that current histological response evaluation based on necrosis, fibrosis and viable cells could not predict clinical outcomes after radiotherapy for extremity soft tissue sarcoma. A significant proportion of patients with a good response after pre-operative radiotherapy present a metastatic recurrence.