Tests local treatment while continuing breast cancer medicines
Tests local ablative therapy while continuing the same drugs, in adults with spreading breast cancer.
Plain-language title generated from the registry record
Registry title: COntinue the SaMe Systemic Therapy After Local Ablative Therapy for Oligo Progression in Metastatic Breast Cancer - the COSMO Study
Key facts
- Where
- Alkmaar, Amsterdam, Arnhem, Deventer, Goes, Groningen, and Utrecht, NetherlandsSee the 7 sites
- Phase
- Phase 2
Where in Netherlands
- Noordwest ZiekenhuisgroepAlkmaar, NetherlandsTaking people
- Antoni van LeeuwenhoekAmsterdam, NetherlandsTaking people
- RijnstateArnhem, NetherlandsTaking people
- Deventer ZiekenhuisDeventer, NetherlandsTaking people
- ADRZGoes, NetherlandsTaking people
- Martini ZiekenhuisGroningen, NetherlandsTaking people
- Antonius ZiekenhuisUtrecht, NetherlandsTaking people
Questions to ask the study team
- How often do I need to come in, and for how long each time?
- Are travel costs paid?
- Can I keep my own doctor?
- What happens if I want to stop?
Trial details
- Who runs it
- The Netherlands Cancer Institute
- Trial code
- NCT05301881
- Record updated
- 11 September 2026
- Original description
Patients with oligoprogression of metastatic breast cancer during palliative treatment that is amenable to local therapy will be included. The local ablative therapy (LAT) may consist of stereotactic ablative radiotherapy (SABR), also known as stereotactic body radiation therapy, surgery or percutaneous ablation.Read full original descriptionShow less
COntinue the SaMe Systemic Therapy After Local Ablative Therapy for Oligo Progression in Metastatic Breast Cancer - the COSMO Study
Patients with oligoprogression of metastatic breast cancer during palliative treatment that is amenable to local therapy will be included. The local ablative therapy (LAT) may consist of stereotactic ablative radiotherapy (SABR), also known as stereotactic body radiation therapy, surgery or percutaneous ablation.
Inclusion: Histologically confirmed invasive breast cancer; Metastatic breast cancer; o Oligoprogression is defined as an increase of ≥20% in size or, in case of FDG-PET-CT, metabolic activity (≥20% in SUVmax) involving a maximum of two lesions. These lesions may consist of: 1 or 2 distant metastatic lesions limited to 1 organ, the primary tumor or locoregional lymph nodes; 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; Lesion(s) must be amenable to resection, radiotherapy or percutaneous ablation with the intent of local obliteration; The radiological imaging that shows progression must be performed within 70 days 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; Lymph nodes should be larger than 15 mm upon first detection of oligoprogression to be classified as progressive; Oligo-progression has to be confirmed with a FDG-PET-CT-scan 5-7 weeks after the initial scan that showed oligoprogression; 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: 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; 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; 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.