Axillary Radiotherapy or Axillary Lymph Node Dissection in Patients With Clinically Node- Positive Breast Cancer Undergoing Upfront Tailored Axillary Surgery

Inclusion Criteria at screening:

* Written informed consent according to ICH/GCP regulations prior to any trial specific procedures.
* Patients ≥ 18 years of age.
* Node-positive breast cancer (histologically or cytologically proven both in primary tumor and in lymph node) American Joint Committee on Cancer/ International Union Against Cancer (AJCC/UICC) stage II-III (all molecular subtypes allowed).
* Node-positivity detected by imaging and non-palpable (iN+) and confirmed by pathology.
* Node-positivity palpable (cN1-3) and confirmed by pathology.
* Occult breast cancer is allowed, if biopsy-proven axillary lymphatic metastasis is present.
* Eligible for primary ALND or SLN procedure and either:

  * Newly diagnosed.
  * Isolated in-breast recurrence or second ipsilateral breast cancer after previous breast conserving surgery and sentinel procedure and at least 3 years disease free and no prior axillary dissection or axillary RT.
* Upfront surgery setting.
* Most suspicious axillary lymph node clipped. (If clipping is not part of the routine, this should be done after consent of the patient as a study procedure.)
* Ability to complete the QoL questionnaires.
* WHO performance status 0-2
* Adequate condition for general anesthesia, breast cancer surgery and radiotherapy.
* Adult patients (≥18 years of age).
* Women of child-bearing potential are using effective contraception (condom, diaphragm, intrauterine device), are not pregnant or lactating and agree not to become pregnant during trial treatment (until end of RT) and thereafter during the time recommended by the guidelines - also for adjuvant systemic therapies. A negative pregnancy test before registration is required for all women of child-bearing potential.
* Men agree not to father a child during trial treatment and for 6 months afterward.

Exclusion criteria at screening:

* Stage IV breast cancer.
* Clinical N3c breast cancer without axillary disease (clinical N3a and clinical N3b are allowed).
* Clinical N2b breast cancer (clinical N2a is allowed).
* Contralateral breast cancer within 3 years.
* Prior axillary surgery (except prior sentinel node procedure in case of in-breast recurrence).
* Prior regional radiotherapy.
* Neoadjuvant treatment with the exception of bridging therapy given for less than 3 months.
* History of hematologic or primary solid tumor malignancy, unless in remission for at least 3 years from pre-registration with the exception of adequately treated cervical carcinoma in situ or localized non-melanoma skin cancer.
* Any other serious underlying medical, psychiatric, psychological, familial or geographical condition, which in the judgment of the investigator may interfere with the planned staging, treatment and follow-up, affect patient compliance or place the patient at high risk from treatment-related complications.

Exclusion criteria at randomization (intraoperatively):

* Absence of clip in the specimen radiography.
* Palpable disease left behind in the axilla after TAS.
* No SLN identified in the axilla.