3650 - A Retrospective Study of Outcomes of Patients with Pleomorphic Dermal Sarcoma Receiving Adjuvant Radiotherapy

H. Fernando¹, E. Chmiel¹, R. Awad², W. Pilch², S. Karanth², N. Sharma², and J. McArdle²; ¹Peter MacCallum Cancer Centre, Melbourne, Australia, ²Royal Hobart Hospital, Hobart, Australia

Purpose/Objective(s): Pleomorphic dermal sarcoma (PDS) is a rare type of skin cancer that often recurs after surgery. Previous studies with small sample sizes have shown local recurrence rates between 7-28%. It is unclear whether adjuvant radiotherapy (RT) following surgery can improve outcomes. The purpose of our study is to investigate the effectiveness of adjuvant radiotherapy in treating PDS. We hypothesise that adjuvant RT improves local control. Materials/

Methods: This study analysed patients with PDS at one institution between 2012 and 2023. Kaplan-Meier analysis was used to calculate local recurrence, distant recurrence, and overall survival.
Results: Out of the 21 cases of PDS that were diagnosed, 14 patients were given adjuvant radiation while 7 were not. The majority of patients were male (76.2%) with an average age of 74.1. All tumours were located in the head and neck region, with the scalp being the most common site (76.2%). After a median follow-up period of 19 months, only one patient was found to have a local recurrence. This patient had narrow margins during the initial excision, without adjuvant radiation, and the recurrence occurred after 5 months. The patient was subsequently treated with re-excision and adjuvant radiotherapy. None of the remaining 6 patients who were managed with surgery alone developed a recurrence, and all of these patients did not have invasion to aponeurosis or skeletal muscle. In the radiotherapy group, there were 6 patients (43%) who had invasion to aponeurosis or skeletal muscle and 5 patients (36%) with narrow margins. There were no local recurrences in this group. Non-healing ulcers were found in 2 patients (14%) in the radiotherapy group and 2 patients (29%) in the surgery alone group. The distant recurrence rate was 21.4% in the radiation group and 0% in the no radiation group. The median overall survival was 57 months.
Conclusion: Adjuvant RT should be considered for PDS for improved local control especially if there are additional risk factors such as narrow margins and deep invasion into aponeurosis/skeletal muscle. However, if there is no involvement of the aponeurosis or a close margin, it may be appropriate to omit radiotherapy. Further investigation is warranted to determine if RT can be safely omitted in low risk patients.