A retrospective study on the comparision of pathological tumour necrosis of conventional versus ultrahypofractionated preoperative radiotherapy in localised extremity soft tissue sarcoma and its correlation with clinical outcomes: A retrospective study on the comparision of pathological tumour necrosis of CONV-RT versus UHYPO-RT preoperative radiotherapy in localised extremity soft tissue sarcoma and its correlation with clinical outcomes.

Background and purpose: We aimed to determine if ultra-hypofractionated radiotherapy (UHYPO-RT) delivering 6Gy x 5 fractions yields similar tumour necrosis compared to conventional radiotherapy (CONV-RT) with 2Gy x 25 fractions in soft tissue sarcoma (STS). The clinical significance of tumor necrosis on loco-regional recurrence-free survival (LRFS), distant disease-free survival (DDFS), and overall survival (OS) were assessed.

Materials and methods: Patients with localised STS treated with CONV-RT or UHYPO-RT followed by surgery were included. Good response was defined as tumour necrosis ≥ 90%, and poor response as < 90%. Mann-Whitney U-test compared median tumour necrosis. Chi-squared analysis was used for categorical variables. Kaplan-Meier function estimated LRFS, DDFS, and OS.

Results: A total of 64 patients received CONV-RT, and 45 received UHYPO-RT. The median tumour size was 7.0 cm, with the lower extremity being the most common site (55%). Myxofibrosarcoma (39%) and undifferentiated pleomorphic sarcoma (16%) were the most frequent histologies. The median time from radiotherapy to surgery was 35 days. There was a significant difference in median tumour necrosis between CONV-RT and UHYPO-RT, with rates of 40% and 60%, respectively (p = 0.022). Patients receiving UHYPO-RT had a higher percentage of tumour necrosis at the 90% cutoff, achieving 27% compared to 6% for CONV-RT (p = 0.003). In a median follow-up of 32 months, 12 patients (9%) experienced loco-regional recurrence, 24 patients (19%) faced distant failure, and 19 patients (15%) died from metastatic disease. Patients with < 90% necrosis had higher rates of loco-regional (13% vs. 0%, p = 0.207) and distant failure (25% vs. 0%, p = 0.021). Three-year LRFS was 86% for < 90% necrosis and 100% for ≥ 90% necrosis (p = 0.160). DDFS was 75% for < 90% necrosis versus 100% for ≥ 90% (p = 0.036). OS rates were 79% and 93%, respectively (p = 0.290).

Conclusion: Preoperative RT with UHYPO-RT was associated with a higher rate of tumour necrosis ≥ 90% than CONV-RT. Our data suggest that more extensive necrosis is associated with better clinical outcomes.