Omission of Breast Surgery for Breast Cancer Patients With pCR on MRI and Vacuum-assisted Biopsy After NST (OPTIMIST)

Inclusion Criteria: * Sex: female * Age: 20 years and older * Patients with no clinical/radiologic distant metastasis * Tumor type: Invasive ductal carcinoma * Tumor subtype: HER2 positive(including luminal B type, triple negative * Extent of disease: initial tumor size ≤ 5cm, cN0-2 * Patients with measurable tumor size * Patients who are expected to achieve pCR after neoadjuvant chemotherapy (MRI size ≤ 1.0 cm AND L-to-B SER ≤ 1.6) * Patients with clip inserted to the primary tumor site before or during neoadjuvant chemotherapy * Patients with informed consent who are competent to make a voluntary decision Exclusion Criteria: * Multifocal lesion (≥2) * Extent of residual microcalcification after neoadjuvant chemotherapy \> 2cm * Bilateral breast cancer or inflammatory breast cancer * Contraindication to radiotherapy * History of previous contralateral breast cancer * Breast cancer patients with distant metastasis * Allergic history to MRI contrast * Male breast cancer * Patients incapable of giving informed consent owing to poor general conditions * Patients with BRCA mutation * Patients willing to receive breast surgery * Patients with a history of cancer diagnosis within 5 years (However, skin cancer other than melanoma and breast carcinoma in situ other than ductal carcinoma in situ can be registered even if 5 years have not passed since the diagnosis)