Local Therapy for ER/PR-positive Oligometastatic Breast Cancer

Inclusion Criteria: * Female sex * ≥ 18 years of age * Histologically confirmed invasive breast cancer, with oligometastatic disease defined as one of the following criteria: 1) One to four bone lesions; 2) One to four lung and/ or hepatic lesions; 3) Distant metastasis limited to ipsilateral cervical lymph nodes; 4) Distant metastasis limited to contralateral axillary lymph nodes * Oligometastatic sites amenable to treatment with a local therapy modality, including surgical resection, stereotactic radiotherapy, or radiofrequency ablation * Estrogen receptor-positive and/ or progesterone receptor-positive breast cancer * Partial response or stable disease after at least six months of systemic therapy for breast cancer * Eastern Cooperative Oncology Group (ECOG) performance status 0 or 1 * Measurable or non-measuble disease according to Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 * Life expectancy of at least 12 weeks * For women in childbearing age, negative pregnancy test until 21 days before the date of study enrollment. * Signed informed consent form * Disposition and aptitude to fulfill the study protocol during the study duration Exclusion Criteria: * HER2-positive breast cancer * Progressive disease during the last systemic treatment received for metastatic disease * Previous local therapy for distant metastasis * Current or previous history of severe diseases, such as clinically relevant heart failure, acute myocardium infarction in the last six months, chronic obstructive lung disease, HIV infection, chronic active hepatitis B or C infection, current serious uncontrolled infections or other severe diseases that may impact patients' expected survival) * Current or previous history of other invasive malignancy within the last five years, excluding non-melanoma skin cancer