Inclusion Criteria:

          1. Woman aged >50 years,

          2. Postmenopausal Status; Note: Note: woman is considered post-menopausal if she has had
             amenorrhea for 12 months or more or has undergone surgical oophorectomy.

          3. ECOG performance status ≤2

          4. Microcalcifications on pre-operative mammography, unifocal, ≤25 mm;

          5. Absence of residual microcalcifications on post-operative mammography;

          6. Breast-conserving surgical excision;

          7. Histologically proven DCIS of the breast without an invasive component; Note:
             histological finding of DCIS lesions associated with or developed in a benign breast
             lesion or in case of a classical lobular carcinoma in situ (LCIS) associated with the
             DCIS are accepted.

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

          9. Low or Intermediate nuclear grade; Note: In case of nuclear grade heterogeneity, the
             higher -grade score will prevail.

         10. 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.

         11. Absence of extensive necrosis;

         12. Immunohistochemical characteristics of luminal A subtype: estrogen receptor (ER) ≥10
             %, progesterone receptor (PR) ≥20 %, human epidermal growth factor receptor-2 (HER2)
             negative (0/1+) or 2+ not amplified (confirmed by fluorescent in situ hybridization
             (FISH) or chromogenic in situ hybridization (CISH)), Ki67 <15%.

         13. 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;

         14. Written informed consent;

         15. Affiliation to the French social security.

        Exclusion Criteria:

          1. Endocrine treatment for breast cancer;

          2. Previous diagnosis of DCIS or invasive cancer, (except basal-cell, carcinoma in situ
             of the cervix or endometrium);

          3. Synchronous bilateral DCIS;

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

          5. Palpable tumour opacity or bloody nipple discharge;

          6. Histological evidence of multifocality (defined as having more than one distinct focus
             of DCIS with >5 mm of intervening benign breast tissue in one quadrant of the breast);

          7. High nuclear grade, including high nuclear grade in heterogeneous tumours;

          8. Associated microinvasive component;

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

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

         11. 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.