• Women, aged ≥ 18 years

• Invasive HR positive/Her2 negative, Her2+ (ER/PR +/-) or TN breast cancer

• Concurrent DCIS in pre-NST biopsy is allowed if there is no suspicion of extensive component i.e. absence of non-mass enhancement on pre-NST MRI, contrast-enhanced mammography or breast-specific gamma imaging and/or absence of calcifications on pre-NST mammography

• Primary tumour (T) clinical stage cT1-2

• Unifocal disease; confirmed by pre-NST MRI, contrast-enhanced mammography or breast-specific gamma imaging

• Clinical nodal stage 0; absence of lymph node metastases should be confirmed by ultrasound or FDG-PET/CT

• Neoadjuvant systemic treatment (NST)

• Marker placed in breast tumour prior to NST

• Breast conserving surgery performed, i.e. no mastectomy

• Sentinel node biopsy performed before or after NST

• Pathologic complete response in breast and lymph nodes, i.e. no residual tumour cells or DCIS detected

• Written informed consent