2670 - Stereotactic Radiotherapy (SRT) with Maintenance Systemic Therapy vs. Standard-of-Care (SOC) Systemic Therapy for Oligoprogressive ER-Positive, HER2-Negative Breast Cancer (AVATAR II)

E. Connolly¹, M. White², S. Siva¹, M. Bressel³, J. Tan¹, K. Byrne¹, D. Day², A. McCartney², K. Webber², and S. P. David¹; ¹Peter MacCallum Cancer Centre, Melbourne, VIC, Australia, ²Department of Oncology, Monash Health, Melbourne, VIC, Australia, ³Peter MacCallum Cancer Centre and Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, VIC, Australia

Purpose/Objective(s): The AVATAR I Trial[1] demonstrated that oligoprogressive luminal (ER positive, HER2 negative) advanced breast cancer patients undergoing established first-line systemic therapy for metastatic disease benefited from SRT as second-line therapy along with their original systemic treatment. A modified PFS, defined as a disease progression not amenable to SRT treatment, was reported as 10.4 months. Given this result, this trial in progress seeks to assess if SRT combined with systemic therapy CDK4/6 inhibitor and Aromatase Inhibitor (CDK4/6+AI) can improve the Quality of Life (QoL) for this cohort of patients. Materials/

Methods: AVATAR II is a Phase 2 randomised control trial that enrols patients with advanced luminal breast cancer who have received first-line systemic treatment in the metastatic setting with a CDK4/6+AI. Patients require at least 1 extracranial oligoprogressing lesion amenable to SRT. Patients who had chemotherapy for metastatic disease, leptomeningeal disease,or prior radiotherapy to an oligoprogessing lesion were excluded. Patients were randomised to Arm A; SRT to all oligoprogressing lesions and continue CDK4/6+AI systemic therapy or Arm B; no SRT and review to assess if a change in systemic therapy is required. If a patient subsequently progresses, further SRT was permitted to delay a change in systemic therapy in patients who had received SRT as part of the trial. At 3-monthly reviews, patient reported outcomes are measured using the EORTC QLQ C30 and FACT-B forms.The trial is expected to recruit 74 patients. The primary endpoint is the area under the curve (AUC) of the Quality of Life/Global Health Status score from the EORTC QLQ-C30 from baseline to the 12-month follow-up visit. The secondary endpoints are to determine Progression-free Survival (PFS) and PFS 2, defined as the time from randomisation to the date of first and second evidence of progression, respectively. Other secondary endpoints include ST-PFS, defined as randomisation to the first evidence of progression requiring change in systemic therapy, Overall Survival, treatment-related toxicity and further QoL assessment using AUC of the FACT-B Total score from baseline to 12 months.
Results: TBD
Conclusion: Assessing quality of life (QoL) is integral to evaluating the overall impact of cancer treatment. AVATAR II aims to demonstrate that by delaying a change in systemic therapy and potentially more potent side effects, receiving SRT at this stage in a patient’s treatment paradigm will have a more positive impact on patients QoL. [1] David SP, Siva S, Bressel M, Tan J, Hanna GG, Alomran RK, et al. Stereotactic Ablative Body Radiotherapy (SRT) for Oligoprogressive ER-Positive Breast Cancer (AVATAR): A Phase II Prospective Multicenter Trial. International journal of radiation oncology, biology, physics. 2023;117(4):e6-e.