Patterns of local recurrence and risk of skin recurrence in soft tissue sarcomas after surgical resection.

Soft tissue sarcomas (STSs) are rare, heterogeneous tumors primarily managed surgically with radiotherapy (RT) added to improve local control. Although there is a theoretical risk of skin seeding at the time of surgery, current ASTRO Clinical Practice Guidelines recommend against routine use of bolus during pre-operative or post-operative radiotherapy for STS due to increased risk of skin toxicity without clear benefit. However, in the modern era with contemporary treatment planning techniques, the risk of skin recurrence has not been assessed. We performed a detailed analysis of the patterns of local recurrence (LR) in patients with STS treated with surgical resection with or without RT.We performed a retrospective analysis of 206 adult patients with extremity or trunk STSs evaluated in the Department of Radiation Oncology at our institution over 14 years (2007-2021) and identified all patients with LR. The depth of the recurrence and location relative to the radiation field in patients treated with radiotherapy was evaluated. Progression free survival (PFS) and overall survival (OS) were analyzed using the Kaplan-Meier method, and cumulative incidence of distant metastasis (CIDM) was calculated with competing risk analysis from the date of LR.Of the 206 patients evaluated, 20 experienced a LR after surgical resection with or without RT. Among patients with a LR, 5 patients (25.0%) were treated with surgery alone and 15 patients (75.0%) received surgery and RT. In patients treated with RT, 46.7% had pre-operative RT, 53.3% had post operative RT, and bolus was used in 5 patients (33.3%). Surgical margins were close (<1mm) in 4 patients (20.0%) and positive in 10 patients (50.0%). Tumor grade was intermediate/high in 15 patients (75%) and the median tumor size was 9 cm (range 5-12). LR occurred in the muscle in 8 patients (40%), subcutaneous tissue in 11 patients (55.0%), and skin in 1 patient (5.0%). The patient with a skin recurrence was treated with surgery alone and the tumor involved the skin at presentation. In the patients treated with RT, LR occurred within radiation field in 10 patients (66.7%). Median follow up time after local recurrence was 12.9 months. At 3 years after LR, PFS was 43.9%, OS was 81.7%, and CIDM was 16.7%.Skin recurrences were exceedingly rare after surgical resection of STSs, and only occurred in a tumor that involved the skin at initial presentation. Due to the increased dose to the normal skin and subcutaneous tissues when bolus is used, which increases risk of toxicity, these findings support current recommendations against routine use of bolus in STSs not involving the skin at presentation.