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NCT Number: NCT06882499

Stereotactic Ablative Body Radiotherapy (SABR) With Maintenance of Systemic Therapy Versus Physicians' Choice of Systemic Therapy for Oligoprogressive ER-positive, Her-2 Negative Breast Cancer II

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.

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Key information

Conditions

Breast Cancer, Metastatic Breast Diseases Breast Neoplasms Metastatic Breast Cancer Neoplasm Metastasis Neoplasms Neoplasms by Site Neoplastic Processes Pathologic Processes Pathological Conditions, Signs and Symptoms Skin Diseases Skin and Connective Tissue Diseases

Age range

18 year and older

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

About this study

AVATAR II is a phase II multicentre open label, randomised trial. Following informed consent, eligible patients with ER-positive, HER2-negative advanced breast cancer receiving an ET (either AI or selective estrogen receptor degrader in combination with a CDK 4/6 inhibitor with newly diagnosed OPD amenable to SABR will be randomised to either:

Arm A: SABR to all known sites of OPD with continuation of first line therapy ET and CDK 4/6 inhibitor Arm B: Physician's choice of systemic treatment

Patients must have evidence of radiological response to ET and CDK 4/6 inhibitor for a minimum of six months prior to randomisation (defined as either stable disease or partial response).

All patients will be followed up for 3 years after the last patient has been randomised.

Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

Patients will be eligible for inclusion in this trial if all the following criteria apply:

  • 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.)
  • Patients must have evidence of radiological response to ET and CDK 4/6 inhibitor for a minimum of six months prior to randomisation (defined as either stable disease or partial response).

Note: Patient must have ongoing stability/response in at least one lesion at the time of randomisation.

  • Evidence of new or existing OPD, as determined by the Investigator and defined according to RECIST1.1 (33), via CT on a per-lesion basis (between 1-5 metastases, including the primary) as follows:
  • At least a 20% increase in the diameter of a lesion, taking as reference the smallest diameter on a previous CT scan with an absolute increase of at least 5mm
  • Appearance of a new lesion(s) Note: A new lesion can be identified using various imaging modalities, such as PET-CT or WBBS, as long as the lesion is visible on serial CT scans.
  • For patients with liver or lung metastases, maximum of 3 oligoprogressive lesions in single organ
  • All OPD must be amenable to SABR, as per the radiotherapy guidelines in section 11.1 and Appendix 4 and 5
  • ECOG performance status 0-2
  • Life expectancy ≥ 6 months
  • Clinician and patient are willing to continue current line of therapy
  • Patient is able to complete QoL questionnaires, and other assessments required as part of the study

Exclusion criteria

Patients will not be eligible for inclusion in this trial if any of the following criteria apply:

  • 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
  • Evidence of lesion within femoral bone requiring surgical fixation
  • Patients with risk of bone fracture are not candidate for SABR (Appendix 4 and 5)
  • Previous chemotherapy for metastatic disease Note: chemotherapy for primary breast cancer is allowed
  • Contraindications to radiotherapy
  • Any condition deeming the patient unsuitable to comply with the study
  • Substantial overlap with previously treated area. Reirradiation is permitted with the condition that the combined plan adheres to the specific dose constraints outlined in this protocol. It is advised to use biological effective dose (BED) calculations to correlate previous doses with the tolerance doses documented in the protocol
  • Evidence of progression in more than 5 lesions
  • Prior SABR delivered for oligoprogressive disease with the intent of delaying a change in systemic therapy.

Treatment and study plan

stereotactic ablative radiotherapy

Radiation

Stereotactic Ablative Radiotherapy

Physician's choice of systemic treatment

Other

Physician's choice of systemic therapy does not mandate a change in systemic therapy, however, SABR is not permitted for management in this arm

Primary outcomes

  1. Primary Outcome Measure

    Time frame: Time from randomisation to progression of disease resulting in a failure of treatment strategy or death by any cause assessed until withdrawal of consent, death, or 3 years after the last patient has been randomised, whichever is earlier.

    The primary endpoint of this study is to measure the time to treatment failure between Arm A and Arm B.

    Treatment failure is defined as time from randomisation to progression of disease resulting in a failure of treatment strategy or death by any cause.

    Progression, will be determined by the Investigator, using the Response Evaluation Criteria in Solid Tumors, Version 1.1. (RECIST1.1; Appendix 2) (33) as a guide.

    The treatment strategy in Arm A is to maintain patients on current ET 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 systemic therapy alone.

Secondary outcomes

  1. Secondary Objective 1

    Time frame: Time from randomisation to progression of disease resulting in a failure of treatment strategy or death by any cause assessed until withdrawal of consent, death, or 3 years after the last patient has been randomised, whichever is earlier.

    To compare PFS; PFS is assessed from randomisation to the date of the first evidence of progression or death by any cause. Progression will be assessed by the treating clinician as part of standard-of-care practice, using RECIST 1.1 as a guide or based on clinical progression.

  2. Secondary Objective 2

    Time frame: Time from randomisation to progression of disease resulting in a failure of treatment strategy or death by any cause assessed until withdrawal of consent, death, or 3 years after the last patient has been randomised, whichever is earlier.

    To compare progression-free survival 2 (PFS-2); PFS-2 is assessed from randomisation to the date of progression on next line of systemic anti-cancer treatment or death by any cause.

  3. Secondary Objective 3

    Time frame: Time from randomisation to progression of disease resulting in a failure of treatment strategy or death by any cause assessed until withdrawal of consent, death, or 3 years after the last patient has been randomised, whichever is earlier.

    To compare PFS of next line of treatment (2nd PFS); 2nd PFS is assessed from failure of treatment strategy to progression on next line of systemic anti-cancer treatment or date of death by any cause.

  4. Secondary Objective 4

    Time frame: Time from randomisation to progression of disease resulting in a failure of treatment strategy or death by any cause assessed until withdrawal of consent, death, or 3 years after the last patient has been randomised, whichever is earlier.

    To compare OS; OS is assessed from randomisation to the date of death by any cause.

  5. Secondary Objective 5

    Time frame: Time from randomisation to progression of disease resulting in a failure of treatment strategy or death by any cause assessed until withdrawal of consent, death, or 3 years after the last patient has been randomised, whichever is earlier.

    To compare treatment related adverse events (TRAEs); TRAEs are adverse events assessed using the Common Terminology for Adverse Events Version 5.0 (CTCAE v5.0) considered possibly, probably, or definitely related to treatment (systemic therapy or SABR)

  6. Secondary Objective 6

    Time frame: Time from randomisation to progression of disease resulting in a failure of treatment strategy or death by any cause assessed until withdrawal of consent, death, or 3 years after the last patient has been randomised, whichever is earlier.

    To compare the QoL using the FACT-B total score: Area under the curve (AUC) of the FACT-B Total score from baseline to 48 weeks

Study contacts

Contact information is provided by the study sponsor or research team.

A/Prof Michelle White

CONTACT

[email protected]

+61 3 9928 8111

A/Prof Steven David

CONTACT

[email protected]

+61 3 9928 9801

Sponsors and collaborators

Lead sponsor

Peter MacCallum Cancer Centre, Australia

Other

Registry information

Acronym: AVATARII

Important dates

Study start
2026
Primary completion
2032
Study completion
2032
First posted
Mar 18, 2025
Registry last updated
Apr 2, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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