The goal of this clinical trial is to assess Stereotactic Ablative Radiotherapy (SABR) as a method to delay a change in systemic therapy in patients with oligoprogressive ER-positive, HER2-negative advanced breast cancer. The main question it aims to answer is to assess whether the addition of SABR to continuation of first line endocrine therapy and CDK 4/6 inhibitor (Arm A) to patients with oligoprogressive ER-positive, HER2-negative advanced breast cancer could have longer time to strategy failure (TSF) in comparison to physician choice of systemic treatment (Arm B) in patients who had progressed first line.
The treatment strategy in Arm A is to maintain patients on current endocrine therapy and CDK 4/6 inhibitor, controlling localised progressing sites of disease with SABR. Treatment strategy in Arm B is to maintain disease control with physician's choice of systemic therapy alone.
Patient has signed the AVATAR-II Patient Information and Consent Form (PICF)
Male or female, ≥ 18 years of age at the time signing consent
Patients with histologically proven ER-positive, HER2-negative advanced breast cancer receiving an ET in combination with a CDK 4/6 inhibitor. Biopsy of metastatic disease if technically feasible but not mandatory
Patients must have evidence of extracranial metastatic disease, with no evidence of uncontrolled intracranial metastases. (Controlled intracranial metastases are defined as stable disease on repeat CT imaging performed at least one month apart.)
Is pregnant or lactating at the time of randomisation
Evidence of more than one clone of metastatic disease e.g., a patient with both ER-positive and triple negative clones of disease And ER-negative and/or HER2-positive disease would be excluded from the study
Evidence of leptomeningeal disease
Evidence of malignant cord compression