Female (both pre- and postmenopausal) or male patients with histologically confirmed ER positive (regardless of PR), HER2 negative breast cancer, according to local pathologist:
• ER-positive defined as ≥ 10% of cells staining positive for ER
• HER2-negative defined as a score of 0, 1+ by immunohistochemistry (IHC) or a negative in situ hybridization (ISH) based on single-probe average HER2 copy number, as per American Society of Clinical Oncology guidelines
• Elevated risk of recurrence after definitive treatment for early breast cancer, defined as:
EITHER:
• Stage IIB or stage III disease according to the 8th edition of the UICC TNM classification and completion of adjuvant chemotherapy.
• OR:
• Completion of at least 4 cycles of neoadjuvant chemotherapy and residual tumour at surgery of ≥ 1cm (≥ypT1c) or axillary node + (ypN+). Patients with only residual micrometastases (N1mic) or isolated tumour cells (ITCs) will not be eligible.
• Age ≥18 years
• Patients must have received at least 4.5 years and up to 7 years of ET and planned to continue adjuvant ET during ctDNA screening phase
• Previous adjuvant CDK4/6 inhibitor or PARP-inhibitor treatment is allowed
• Available FFPE tumour block with 25mm2 minimum surface from the baseline biopsy or from surgical specimen OR preferably 6-10 unstained slides of 10μm each (or 12-20 unstained slides at 5μm each) PLUS one H&E slide. Tumour cellularity must be ≥ 20% (preferably ≥30%).
Note: Sequencing of tumour tissue is necessary to build a patient specific ctDNA assay. Patients from whom tumour tissue is not available cannot be registered in the study
• Before patient registration, written informed consent must be given according to ICH/GCP, and national/local regulations