Continuing systemic therapy after local treatment for metastatic breast cancer

COntinue the SaMe Systemic Therapy After Local Ablative Therapy for Oligo Progression in Metastatic Breast Cancer - the COSMO Study

Phase 2 Interventional The Netherlands Cancer Institute · NCT05301881

This study is testing if continuing treatment after local therapies can help people with metastatic breast cancer feel better and live longer.

Quick facts

PhasePhase 2
Study typeInterventional
Enrollment118 (estimated)
Ages18 Years and up
SexAll
SponsorThe Netherlands Cancer Institute Academic / other
Drugs / interventionsPertuzumab, trastuzumab, chemotherapy, radiation
Locations7 sites (Alkmaar and 6 other locations)
Trial IDNCT05301881 on ClinicalTrials.gov

What this trial studies

This study focuses on patients with oligoprogression of metastatic breast cancer who are undergoing palliative treatment. It evaluates the effectiveness of continuing systemic therapy after local ablative therapies such as stereotactic ablative radiotherapy, surgery, or radiofrequency ablation. Patients must have stable disease or a partial/complete response to systemic therapy for at least six months before oligoprogression is detected. The goal is to determine if ongoing systemic treatment can improve outcomes for these patients.

Who should consider this trial

Good fit: Ideal candidates include patients with histologically confirmed invasive metastatic breast cancer experiencing oligoprogression after at least six months of systemic therapy.

Not a fit: Patients with widespread metastatic disease or those who have not responded to systemic therapy for the required duration may not benefit from this study.

Why it matters

Potential benefit: If successful, this approach could enhance treatment outcomes and prolong survival for patients with oligoprogressive metastatic breast cancer.

How similar studies have performed: Other studies have shown promise in similar approaches, but this specific methodology is relatively novel.

Eligibility criteria

Show full inclusion / exclusion criteria
Inclusion Criteria:

* Histologically confirmed invasive breast cancer
* Metastatic breast cancer
* Oligoprogression defined as one or two distant metastatic lesions, limited to one organ, or the primary tumor or locoregional lymph nodes, increasing ≥20% in size and be larger than 15 mm or if metabolic activity increases (with 20% in SUVmax) on FDG-PET-CT.
* Systemic treatment can be either endocrine, targeted, chemotherapy or immune-checkpoint blockade
* Patients should be on systemic therapy for at least six months. Status should be stable disease or partial or complete response for at least 6 months.
* Oligoprogression has to be detected with radiological imaging comparing the lesion on the same type of imaging modality as has been used at the start of systemic therapy.
* The radiological imaging that shows progression must be performed within 70days prior to LAT.
* Bone metastases are classified as progressive if the lytic component of the lesion increases by ≥20% or the FDG-uptake increases by ≥20% on FDG-PET-CT
* Oligo-progression has to be confirmed with a FDG-PET-CT-scan 5-7 weeks after the initial scan that showed oligoprogression.
* Lesion(s) must be amenable to resection, radiotherapy or radiofrequency ablation with the intent of local obliteration
* Age ≥18
* World Health Organization (WHO) Performance Status 0 or 1
* Signed written informed consent before patient registration according to ICH/GCP, and national/local regulations

Exclusion Criteria:

* Having received more than two lines of systemic therapy for MBC If a treatment regimen has been de-escalated without adding other therapies, this is seen as one line of therapy. For example: Pertuzumab/trastuzumab+docetaxel followed by pertuzumab/trastuzumab will be viewed as one line of systemic therapy.
* Other malignancy except carcinoma in situ and basal-cell and squamous cell carcinoma of the skin, unless the other malignancy was treated ≥5 years ago with curative intent without the use of chemotherapy or radiation therapy
* Current pregnancy or breastfeeding. Women of childbearing potential must use adequate contraceptive protection
* Presence of any medical condition that would place the patient at unusual risk, up to the discretion of the clinician
* Presence of any psychological, familial, sociological, or geographical condition potentially hampering compliance with the study protocol and follow-up schedule

Where this trial is running

Alkmaar and 6 other locations

Study contacts

How to participate

  1. Review the eligibility criteria above with your treating physician.
  2. Visit the official trial page on ClinicalTrials.gov for the most current contact information and recruitment status.
  3. Contact the listed study coordinator or principal investigator to request pre-screening. Pre-screening is free and never obligates you to enroll.
Conditions Breast Cancer InvasiveMetastatic CancerOligoprogressive
Last reviewed 2026-06-13 by the Find a Trial editorial team. Information on this page is for educational purposes and is not medical advice. Always consult qualified healthcare professionals about clinical trial participation.