(P 277) THE ROLE OF RADIOTHERAPY IN THE MULTIDISCIPLINARY MANAGEMENT OF RADIATION-ASSOCIATED ANGIOSARCOMA OF THE BREAST: A REFERRAL CENTER EXPERIENCE

Objective: Radiation-associated angiosarcoma (RAAS) of the breast is a rare and aggressive disease, occurring as a late complication of adjuvant radiotherapy (RT) for primary breast cancer (BC). To date, the role of RT in RAAS is unclear and controversial. In this retrospective study, we evaluated the role of RT within a multidisciplinary (MD) treatment of patients who underwent surgery at a referral center.

Methods: Cases of resectable histologically-proven RAAS, evaluated by a MD team were analysed. RT was given either preoperatively (Preop) +/- chemotherapy (CT) or postoperatively (Postop). RT treatment details and toxicity profiles according to CTCAE scale v5 were collected. Overall and disease-free survival (OS, DFS) data were analysed using Cox models and estimating Kaplan-Meier curves. Inverse probability weighting with propensity scores was used to account for groups’ differences in baseline characteristics.

Results: From March 2010 and October 2023, 27 patients (median age 69.8 years) were identified. All of them had received postop RT for primary BC. The interval between prior breast RT and RAAS was 7.6 years (4.69; 11.17). Thirteen patients received Postop RT (dose 50-60Gy in 25-30 fractions). Fourteen patients received Preop RT (dose 44-50.4Gy in 22-28 fractions): 7 sequentially to CT and other 7 concurrent CT-RT. Median follow-up was 36.81 months. The adjusted 5-year OS were 73.04% and 53.6% for postop RT and preop RT, while 5-year DFS were 75.2% and 53.8%, respectively. Overall, 5 patients experienced a local recurrence with a 12, 24-month crude cumulative incidence of 3.7% and of 20.42%, respectively. Patients receiving preop RT appeared to have a higher risk of death and recurrence than postop RT group (hazard ratios: 2.17-p=0.395, and 2.71-p=0.182, respectively). In the postop RT group were observed significantly longer time interval to prior RT (p=0.0198) and higher rates of total mastectomies (p=0.0001). Regarding acute toxicities, 13 (48%) G2 skin, 1 (3.7%) G3 skin toxicity and 1 (3.7%) G2 pneumonitis were observed. Three (11%) patients developed major wound complications, all of them in the preop RT group. As of late toxicities G1 pneumonitis in 2 (7.4%) patients, rib fracture in 1 (3.4%) patient and cardiac events in 2 (7.4%) patients were observed.

Conclusion: The findings of this study support that RT within a trimodality approach leads to improved local control without increased toxicity for RAAS.