Basket Study for Oligo-metastatic Breast Cancer (ANISE)

Inclusion Criteria: Histologic proof of infiltrating HER2-positive breast cancer (as determined by IHC 3+ and/or amplification by ISH)[8] Histologic or cytologic proof of breast cancer metastases (at least one lesion) Histologic determination of level of ER-expression Oligo-metastatic disease as determined by standard of care diagnostics. The number of total individual distant metastases is limited to three, either in one organ or in 2-3 organ systems. Clustered lymph nodes that can be irradiated with curative intent in a single field are defined as single lesion. Pleuritis carcinomatosa, miliary spread of metastases (even within one organ), or peritoneal spread of metastases rules out oligo-metastatic disease and is not allowed. Initial staging by PET-CT (whole body) and MRI of breast and brain are mandatory, as is MRI liver or spine and pelvis in case of liver or bone metastases respectively. In case of recurrent disease, a disease-free interval of 24 months. Measurable disease according to RECIST1.1 Patients must be at least 18 years of age and be able to give written informed consent and comply with study procedures. World Health Organization (WHO) performance status 0 or 1 Exclusion Criteria: prior line of therapy for metastatic disease. Exceptions are endocrine therapy or radiation considered to be part of the curative treatment, within 3 months before enrolment leptomeningeal disease or central nervous metastases clinically relevant obstruction or compression of spinal cord, central nervous, gastro-intestinal or cardiovascular system, that cannot be alleviated before start of treatment. other malignancy, unless treated with curative intention and a long-term survival probability of >95%, including in-situ or pre-malignant lesions.