The standard treatment of localized breast cancers consists of surgical removal of the tumor at the breast or removal of the entire breast and lymph nodes (sentinel lymph node and / or axillary dissection) with or without chemotherapy followed by radiotherapy on the breast or thoracic wall and the lymph node areas from 5 to 6.5 weeks.

Shorter radiotherapy treatments over 3 weeks for breast cancer without lymph node involvement have been equally effective and have no more side effects in several clinical trials involving several thousand patients. This called hypofractionated radiotherapy has become a standard for breast cancers in the absence of lymph node involvement in postmenopausal women.

The objective of the HypoG01 trial is to evaluate hypofractionated radiotherapy in women who require radiotherapy in the breast or chest wall and lymph node areas by comparing standard over 5 to 6.5 weeks and hypofractionated irradiation over 3 weeks analyzing the possible side effects and in particular the risk of lymphedema (swelling of the arm on the side treated) and the effectiveness of these treatments

Inclusion Criteria:

• Woman ≥ 18 years who had radical surgery for invasive breast cancer pT1-3, pN0-N3, M0 with either mastectomy or breast conservation. The patient can be included no matter the status of oestrogen receptor, progesterone receptor, malignancy grade, HER2 status.
• ECOG 0-2
• Axillary lymph node dissection of the axilla where the findings give indication for regional nodes radiotherapy to levels +/-I, +/- II, +/-III, +/-IV, +/-interpectoral nodes (Rötter) and +/-the IMN.
• Sentinel node biopsy documenting limited nodal disease without an indication for axillary lymph node dissection according to institutional, national or other trial guidelines are accepted.
• The patient may be a candidate for a boost to the tumour bed.
• Adjuvant systemic therapy with chemotherapy, endocrine therapy and anti-HER2 treatment is accepted.
• Neoadjuvant chemotherapy for downstaging according to institutional or national guidelines is accepted if there is not an indication for a boost in the area of regional nodes after surgery.
• Primary systemic therapy of an operable breast cancer is accepted.
• If the patient is not treated with chemotherapy, the patient must be randomized within 8 weeks from last surgery. If the patient has received adjuvant chemotherapy, the patient must be randomized within 4 weeks after the last series of adjuvant chemotherapy or within 42 days from last surgery in case of surgery after neoadjuvant or adjuvant chemotherapy.Breast implants are accepted.
• Connective tissue disease is allowed if the treating radiation oncologist finds radiotherapy indicated
• Postoperative infection and/or seroma giving indication for drainage during RT is accepted
• Women of childbearing potential must agree to use adequate contraception for the duration of study participation and up to 3 months following completion of therapy
• Signed informed consent
• Affiliated to the Social Security system

Exclusion Criteria:

• Previous breast cancer or DCIS of the breast.
• Bilateral breast cancer
• Patient with previous non-breast malignancy with the exception of cancer in complete remission for over 5 years and low risk of recurrence. Patients with the following diseases can be accepted despite less than 5 years disease free interval: carcinoma in situ of the cervix, melanoma in situ, basal cell carcinoma of the skin, squamous cell carcinoma of the skin
• The patient has an indication for boost to 1 or more regional nodes
• Previous radiotherapy to the chest region
• Patient enrolled in another therapeutic trial. Observational cohorts are accepted if the collection of data does not interfere with the current trial
• Pregnant or lactating
• Conditions indicating that the patient cannot go through the radiation therapy or follow up, or a condition where the treating radiation oncologist thinks the patient should not participate in the trial for example due to language problems.