(P 324) EVALUATING THE ROLE OF ADJUVANT RADIATION AFTER WIDE LOCAL EXCISION OF PLEOMORPHIC DERMAL SARCOMA

Objective: Pleomorphic dermal sarcomas (PDS) are rare undifferentiated mesenchymal tumors that are poorly defined but have adverse histological features and metastatic potential. Treatment is centered around surgical excision; however, the optimal adjuvant treatment regimen is unclear due to its rarity. This study aims to evaluate the impact of adjuvant radiation therapy (RT) on long-term survival in patients with PDS after surgical excision.

Methods: The National Cancer Database was queried to identify patients with PDS who underwent surgical excision. Patients were stratified based on receipt of RT. Demographics, tumor characteristics and treatment type were evaluated. Kaplan Meier method was used to estimate overall survival (OS). Multivariable Cox proportional regression models were performed to identify predictors of OS.

Results: A total of 1442 patients were identified with PDS who underwent surgical excision, with 219 (15.2%) patients who received RT compared to 1223 (84.8%) patients who did not. There was no statistically significant difference in treatment facility type or location, patient gender, race, median household income, or comorbidity scores between the two groups based on receipt of RT or not. Regarding tumor characteristics, patients who received RT tended to have tumors greater than 2cm (58.6% vs 34.7%, P< 0.001), high grade tumors (28.3% vs 11.9%, P< 0.001), presence of lymphovascular invasion (LVI) (5.3% vs 0.7%, P< 0.001), positive regional lymph nodes (3.8% vs 0.4%,P < 0.001), and positive surgical margins (22.8% vs 8.1%, P< 0.001). Patients who received RT were also treated with chemotherapy (4.7% vs 0.7%, p< 0.001) more often than those who did not receive RT. The median OS was higher for patients with small tumors < 2cm compared to those with larger tumors >2cm (84.3 months vs. 41.4 months, P< 0.001). R0 margin status was also associated with significantly improved survival compared to those with positive margins after resection (median OS 82.3 months vs. 43.6 months, P< 0.001). However, adjuvant radiation was not associated with improved survival (median 78 months vs 71 months, P=0.474). Subgroup analysis of patients with R1 margin status after surgery showed no differences in survival with or without radiation (median OS 45 months vs. 41.3 months, p=0.998). On multivariate analysis, older age (HR 1.07, P< 0.001), high comorbidity score (HR 1.71, P=0.014), tumor size (HR 1.60, P< 0.001), and positive margin status (HR 1.68, P=0.001) were independent predictors of poor survival.

Conclusion: Adjuvant RT was not associated with improve survival in resected PDS, regardless of margin status. Due to limited effective systemic treatment options for pleomorphic dermal sarcoma, curative intent complete resection with R0 margins remains the cornerstone of treatment for PDS. While the use of RT in the treatment of PDS was more common in patients with tumors with more aggressive features, there remains limited data to support the use or omission of adjuvant RT in PDS. The role of adjuvant RT should be an area of future investigation, and adjuvant RT should be considered for PDS on a case-by-case basis based on local recurrence risk or potential risk of distant metastases.