ESTRO 2024 - Abstract Book

S2096

Clinical - Sarcoma, skin cancer, melanoma

ESTRO 2024

Purpose/Objective:

Neoadjuvant radiotherapy followed by definite surgery provides excellent local control in soft tissue sarcomas (STS). We aimed to determine if hypofractionated radiotherapy (HYPO-RT) delivering 30Gy in 5 fractions yields similar tumour necrosis compared to conventional radiotherapy (CONV-RT) with 50Gy in 25 fractions in STS and its clinical significance with respect to loco-regional control, distant disease-free survival, and overall survival.

Material/Methods:

We evaluated 124 consecutive patients with localised STS who had pre-operative radiotherapy followed by definite surgery at our institution from 2018 to 2022. Good response is defined as tumour necrosis ≥ 90% and poor response as < 90%. Tumour characteristics including histological subtype, grading, and necrosis were reviewed centrally at our institution. Independent sample median test was used to compare the median necrosis between the two dose fractionation groups. Fisher exact or Chi-squared analysis were used for categorical variables. Loco regional control, distant disease-free survival, and overall survival were estimated using Kaplan-Meier estimate of survival function. Hazard ratio was estimated by the Cox proportional model. Loco-regional failure was defined as disease recurrence at the primary site of disease and/or recurrence at lymph nodes regional to the primary disease site. Distant failure was defined as recurrence at sites other than the primary site and regional lymph nodes

Results:

Overall, 82 (64.1%) of patients were male. Median age was 63.5 (range: 24.0 – 93.0) years. Lower extremity was the most common location, n = 77 (60.2%).

A total of 74 patients had CONV-RT and 54 patients had HYPO-RT. Of the 74 patients treated with CONV-RT; 16.2% had low grade, 36.5% had intermediate grade, 35.1% had high grade, and 12.2% had ungraded tumour. Of the 54 patients who had HYPO-RT; 22.2% had low grade, 37.0% had intermediate grade, 35.2% had high grade, and 5.6% had ungraded tumour. The most common histology across both groups was myxofibrosarcoma (32.8%) followed by myxoid liposarcoma (14.8%), and undifferentiated pleomorphic sarcoma (UPS) (11.7%). The median time from completion of pre operative radiotherapy to surgery for both groups was 35 (range 25 – 62) days. There was a significant difference in median tumour necrosis percentage between CONV-RT and HYPO-RT (40.0% vs 60.0%, p = 0.011). Utilising a cut off of 90% necrosis, patients treated with the hypofractionated regime of had a significantly higher percentage of tumour necrosis compared to the conventional regime (37.0% vs 16.2%, p = 0.007). Within different histological subtypes, patients with UPS, solitary fibrous tumour, and myxoinflammatory fibroblastic sarcoma had significantly higher tumour necrosis with HYPO-RT compared to CONV-RT (p = 0.039, 0.025, 0.046 respectively). During an overall median follow up of 32 months (median follow up for the CONV-RT and HYPO-RT group was 45.5 and 20.5 months respectively); twelve patients (9.4%) developed loco-regional recurrence, 24 patients (18.8%) developed distant failure, and 19 patients (14.8%) died of metastatic disease. All patients who developed distant metastatic disease had ablative radiotherapy if they had oligometastatic disease or systemic treatment if they had extensive disease.