Zapping a few growing tumors may keep breast cancer drugs working longer

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * 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 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