Inclusion Criteria:

          1. Woman aged ≥50 years,

          2. ECOG performance status ≤2

          3. Microcalcifications on pre-biopsy mammography, unifocal, ≤25 mm or opacity without
             microcalcifications and no clinical palpable tumour

          4. Absence of suspicious residual microcalcifications either on post-biopsy/ preoperative
             localization mammography, or on post-operative mammography Note: if absence of
             residual microcalcifications on post-biopsy/pre-operative mammography, post-operative
             mammography is not mandatory;

          5. Breast-conserving surgical excision;

          6. Histologically proven DCIS of the breast without an invasive component; Note
             Incidental histological finding of DCIS lesions developed within a benign breast
             lesion as well as an association with classical lobular carcinoma in situ (LCIS)
             associated with the DCIS are accepted.

          7. Free margins (≥2 mm), or free margins following re-excision;

          8. Low or Intermediate nuclear grade; Note: In case of nuclear grade heterogeneity within
             the same sample or between the biopsy or the surgical specimen, the highest nuclear
             grade score will prevail.

          9. Tumour tissue sample availability; Note: Surgical specimen is mandatory unless no
             residual disease on the surgical specimen. In this instance, the initial diagnosis
             biopsy is required.

         10. Absence of extensive necrosis (≤30% of the lumen diameter);

         11. Immunohistochemical characteristics of luminal A subtype: ER≥10 %, PR ≥20 %, HER2
             negative (0/1+) or 2+ not amplified (confirmed by fluorescent in situ hybridization
             (FISH) or chromogenic in situ hybridization (CISH)), Ki67 <15%.

         12. Patient willing and able to comply with the protocol for the duration of the study
             including undergoing treatment, scheduled visits and examinations and including
             follow-up;

         13. Written informed consent.

         14. Affiliation to the French social security.

        Exclusion Criteria:

          1. Endocrine treatment for breast cancer.

          2. Previous invasive breast cancer including contralateral breast cancer, either
             metachronous or synchronous

          3. Previous DCIS except contralateral DCIS in complete and continuous remission for more
             than 5 years

          4. Previous other cancers (except basal-cell, carcinoma in situ of the cervix or
             endometrium), not in complete and continuous remission for more than 10 years

          5. Known breast-cancer predisposing germ-cell mutation;

          6. Palpable tumour with a diagnosis of DCIS on biopsy

          7. Bloody nipple discharge;

          8. Histological size >25 mm in one or multiple foci

          9. High nuclear grade, including high nuclear grade in heterogeneous tumours;either on
             biopsy or on surgical specimen

         10. Associated microinvasive or invasive component;

         11. Presence of tumour cells in lymph nodes detected using H&E or immunohistochemical
             examination (if lymph node sentinel biopsy or dissection has been performed);

         12. Absolute contra-indication to whole-breast irradiation as determined by the referring
             physician;

         13. Patient unable to comply with study obligations for geographic, social, or physical
             reasons, or who is unable to understand the purpose and procedures of the study.

         14. Pregnant women or breast feeding mothers,