Stereotactic Radiotherapy for Oligoprogressive ER+/HER- Metastatic Breast Cancer, a Prospective Phase 2 Study (Oligopro-Breast)

The Oligopro-Breast Study: Stereotactic Radiotherapy for Oligoprogressive ER+/HER- Metastatic Breast Cancer, a Prospective Phase 2 Study

The Oligopro-Breast trial is a Phase II study targeting women with ER+/HER2- metastatic breast cancer who have been on endocrine therapy and/or CDK4/6 inhibitors for at least 6 months, and show progressive disease at 1-3 extracranial metastases, which are treatable locally. The trial aims to investigate if treating these resistant metastases with SBRT (or other local treatments if SBRT is not possible) can extend the use of the current systemic therapy.

Patients will continue their existing systemic treatment while receiving SBRT on all progressive lesions. If new oligoprogression occurs, SBRT will be performed again. A new systemic treatment line will start if there is polyprogression (more than 3 lesions at once), progression of more than 6 lesions over 12 months, intracranial progression, or lesions that cannot be treated locally.

The scientific question is whether local treatment of resistant metastases can prolong the effectiveness of ongoing systemic therapy, which is particularly beneficial if the treatment is well-tolerated. The primary objective is to measure the proportion of patients surviving without changing their systemic treatment line at 6 months after SBRT.

This trial is significant for patients as it explores a method to potentially extend the duration of effective and well-tolerated treatments, offering hope for better management of metastatic breast cancer.

Study Overview

• Status: Recruiting
• Conditions: OligoProgressive Metastatic Disease
• Intervention / Treatment: Radiation: SBRT

• Study Type: Interventional
• Enrollment (Estimated): 48
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Robbe Van den Begin, MD PhD; Phone Number: +32 2 541 38 28; Email: robbe.vandenbegin@hubruxelles.be

Study Locations

• Belgium
  • Brussels, Belgium
    • Recruiting
    • Jules Bordet Institute
    • Contact: Alex De Caluwé, MD; Phone Number: +32 2 541 38 28; Email: alex.decaluwe@hubruxelles.be
  • Ghent, Belgium
    • Recruiting
    • UZ Gent
    • Contact: Liv Veldeman, MD PhD; Phone Number: +32 9 332 30 15
  • Kortrijk, Belgium
    • Recruiting
    • AZ Groeninge
    • Contact: Isabelle Kindts, MD PhD; Phone Number: +32 56 63 39 03; Email: radiotherapie@azgroeninge.be
  • Mechelen, Belgium
    • Recruiting
    • AZ Sint-Maarten
    • Contact: Alex De Caluwé, MD; Phone Number: +32 15 89 29 80; Email: azsintmaarten@emmaus.be
  • Namur, Belgium
    • Recruiting
    • CHU UCL Namur - Site Saint Elisabeth
    • Contact: Vincent Remouchamps, MD PhD; Phone Number: +32 81 72 05 25; Email: sormn.se@chuuclnamur.uclouvain.be

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• ECOG performance status 0-2.
• Histologically confirmed ER+/HER2- MBC.
• History of polymetastatic disease. Patients with genuine oligometastatic disease and 1-3 oligoprogressive lesions are only allowed if ablative therapy of all metastases is deemed impossible.
• Under 1st to 2nd systemic treatment line with hormonotherapy and/or CDK4/6 inhibitors for at least 6 months before progression.
• Progressive disease at 1-3 extracranial sites.
• Ability to treat all progressive lesions locally according to the treating radiation oncologist.

Exclusion Criteria:

• Second malignancy if it is not in complete remission.
• Previous local treatment for oligoprogression under the current systemic treatment line
• Current progression in a lesion that has been treated with SBRT before and is not amendable for surgery or radiofrequency ablation (RFA).
• Progressive or newly diagnosed brain metastases. Known brain metastases that have been nonprogressive for at least 6 months, are not an exclusion criterion.
• Inability to continue the same ST line after local therapy (for example because of toxicity or patient refusal).
• Pregnancy.
• Inability to sign the informed consent.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: SBRT on the oligoprogressive metastases. Continuation of same systemic therapy.	Radiation: SBRT; SBRT of all oligoprogressive metastases (or other local therapy if SBRT not advisable), followed by continuation of the same systemic therapy.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
NExt Systemic Treatment-Free Survival (NEST-FS)	At 6 months

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Progression-free survival (PFS)		3 years
Overall survival (OS)		3 years
Time to next line of systemic therapy (NEST)		3 years
Modified Progression-free survival (mPFS)	Defined as the survival in the absence of any of the following : (1) polyprogression (progressive disease of more than 3 lesions at the same time), (2) progression of more than 6 lesions over a 12-month rolling period, (3) intracranial progression, (4) progressing lesion that cannot be treated locally, or (5) death.	3 years
Chemotherapy-free survival		3 years
Progression-free survival after start of the subsequent line of systemic treatment (PFS2)		3 year
Patterns of metastatic progression	We defined four patterns of progression: stable disease, progression on untreated pre-existing lesions, progression on treated lesions, or development of new lesions. In case of progression, it will also be determined whether it is oligoprogression (progression of 3 lesions or less) or polyprogression (progression of more than 3 lesions).	3 years
Acute and late physician-scored toxicity of the local intervention	Acute and late physician-scored toxicity of the local intervention (CTCAE 5.0, Early: within 90 days; late: 90 or more days after SBRT);	3 years
Quality of life (QoL)	Evolution of QoL measured with the EORTC QLQ-C30	3 years

Other Outcome Measures

Outcome Measure	Time Frame
Correlation between (1) ctDNA burden at baseline and (2) ctDNA burden 10-12 weeks after SBRT versus the modified progression-free-survival (mPFS). NEST-FS in function of ESR1 status.	3 years

Collaborators and Investigators

• Sponsor: Jules Bordet Institute

Study record dates

Study Major Dates

• Study Start (Actual): October 30, 2025
• Primary Completion (Estimated): May 1, 2028
• Study Completion (Estimated): May 1, 2030

Study Registration Dates

• First Submitted: March 26, 2025
• First Submitted That Met QC Criteria: April 11, 2025
• First Posted (Actual): April 13, 2025

Study Record Updates

• Last Update Posted (Actual): February 2, 2026
• Last Update Submitted That Met QC Criteria: January 30, 2026
• Last Verified: October 1, 2025

More Information

Terms related to this study

• Keywords: radiotherapy; SBRT; metastatic breast cancer; SABR; CDK4/6 inhibitors; Oligoprogression
• Additional Relevant MeSH Terms: Neoplasms by Site; Neoplasms; Skin Diseases; Breast Diseases; Skin and Connective Tissue Diseases; Breast Neoplasms
• Other Study ID Numbers: CE4005

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No