(P 516) OUCOMES OF AGGRESSIVE RESECTION OF RADIATION INDUCED ANGIOSARCOMA OF THE BREAST

Objective: Radiation induced angiosarcoma (RIAS) of the breast is a rare tumor with high rate of local recurrence. Current acceptable treatment is surgical resection in cases of localized disease. There are no strict guidelines regarding the extent of resection. Recent studies have showed that a more extensive or radical resection may reduce the rate of local recurrence. The aim of this study is to evaluate the outcome of radical resection performed at our center.

Methods: A retrospective analysis of all patients who underwent surgical resection for RIAS of the breast between 2007-2022 at a tertiary academic referral center (n=26). Included were patients who have localised disease to the breast (no metastatic disease on staging) and underwent radical resection, includes complete resection of the majority of previously irradiated skin, subcutaneous tissue and underlying fascia of pectoralis major (or muscle resection depending on extent of deep tumour invasion) Post-operative and long-term oncological outcomes were than analyzed.

Results: Twenty-two (n=22) patients met the inclusion criteria. Median age was 73.5 (range, 62-85). Median time from radiation to diagnosis of angiosarcoma was 106 months (range, 50.1-343). The median Charlson comorbidity index was 6 (range 1-8). Of all patients, 5 (22.2%) had their pectoralis fascia removed, 7 (31.8%) had both pectoralis fascia and part of the underlying muscle and 9 (40%) had complete pectoralis major muscle removed during surgery. 4 (18%) patients had reconstruction with local flaps, 12 (54%) with a pedicle flap, and 6 (27%) with a free flap. The rate of post-operative complication was 13.6% (n=3) in which only 1 (45) of them was major and was related to the reconstruction. The mean size of the specimen was 201mm (±58) with a mean size of tumor of 52mm (±27). Most of the patients had a high-grade tumor (grade II in 40%, and grade III in 50%), with 17 patients had a single lesion (77.2%) and 5 (22.7%) with a multifocal disease. One (4.5%) patient received neoadjuvant therapy while 2 (9%) patients received adjuvant therapy. At a median follow-up of 25.4 months (range, 7.9- 95.2), 3 (13.6%) patients had both local and metastatic lung disease and 1 (4%) patient with only lung metastasis. For those patients who recurred, the median time to recurrence was 19.2 months (range, 4.6-24.3). The estimated 3 and 5-year OS was 90.9% and 75.7% respectively, with a median that was not reached (mean 82.6 months). The estimated 3- and 5-year disease free survival rate are both 75.1% with a median that was not reached (mean 78.6 months).

Conclusion: Treatment of RIAS of the breast with an up-front locally aggressive approach is associated with a low rate of local recurrence.