Abstract PO3-22-02: Concurrent chemotherapy with adjuvant radiation for patients with high-risk locally advanced breast cancer: safety and outcomes

Abstract Background: Patients with locally advanced breast cancer are at high risk for locoregional and distant recurrence and novel strategies are needed to enhance the efficacy of adjuvant radiation therapy. Selected chemotherapies act synergistically to safely radiosensitize residual disease to radiation therapy and may improve locoregional control when given concurrently. We report our institutional experience using concurrent chemotherapy with adjuvant radiotherapy for high-risk breast cancer patients. Methods: We conducted a retrospective study of breast cancer patients treated definitively with chemotherapy, surgery, and concurrent chemo-radiation (chemo-XRT) in the adjuvant setting between May 2006 and April 2019. The decision to combine chemotherapy with adjuvant conventionally fractionated radiation was based on provider discretion regarding patient’s risk of recurrence. The primary outcome was risk of locoregional recurrence (LRR). Secondary outcomes included disease free survival (DFS), overall survival (OS), and toxicity. The cumulative incidence of local recurrence was estimated with distant recurrence and death as competing risks. DFS and OS was estimated using the Kaplan-Meier method. Results: A total of 42 patients met inclusion criteria; of these 35 (83%) patients were receiving treatment for their initial breast cancer diagnosis and 7 (17%) patients were receiving treatment for a locoregional recurrence. Of the 35 patients treated in the primary setting, the majority had stage III disease (91%). Twenty-nine patients (83%) received neoadjuvant chemotherapy (NAC) all of which had residual disease after NAC and 6 patients (17%) received upfront primary surgery. Overall median total radiation dose was 57 Gy (range 45-68 Gy) with a majority receiving comprehensive regional nodal irradiation (25, 60%). Chemotherapy agents used for chemo-XRT included capecitabine (29, 69%), paclitaxel (8, 19%), and cisplatin (5, 12%). Median follow-up was 5 years after surgery (range: 4 months-16 years). At 5 years, the cumulative risk of LRR was 7% (95% CI: 2-21%). DFS was 47% (95% CI: 34-65%) and OS was 56% (95% CI: 42-74%). Of note, there were multiple exceptional responders, with OS of 51% at 10 years and 45% at 15 years. Chemo-XRT was well tolerated with 7% grade 3 toxicity (dermatitis), no grade 4 toxicity, and no new toxicity signals observed. Conclusions: Concurrent chemo-XRT for breast cancer patients with high risk locally advanced disease was safe and well tolerated. Chemo-XRT showed promise as a method to decrease risk of locoregional recurrence: the studied patient population was at very high risk, but only 7% of patients had a locoregional recurrence at 5 years. Further prospective evaluation of concurrent chemo-XRT is needed. Table 1. Patient characteristics and outcomes (N = 42) XX- XX Citation Format: Lynn Symonds, Sasha Swenson, Macklin Nguyen, Daniel Hippe, Hannah Linden, Jennifer M. Specht, WIlliam Gwin, Janice Kim. Concurrent chemotherapy with adjuvant radiation for patients with high-risk locally advanced breast cancer: safety and outcomes abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-22-02.