STUDY AIM To decrease the number of breast cancer patients receiving over treatment of the axilla, in order to positively influence the axillary morbidity rate and quality of life.

PRIMARY OBJECTIVE To determine whether omitting the sentinel lymph node procedure is not inferior to the current axillary staging regimen in clinically node negative breast cancer patients undergoing breast conserving therapy, in terms of regional recurrence rate.

HYPOTHESIS The sentinel lymph node procedure can be safely omitted in clinically node negative breast cancer patients undergoing breast conserving therapy. This will lead to a decreased axillary morbidity rate, with a non-inferior regional recurrence-, distant-disease free- and overall survival rates.

Inclusion Criteria:

• Female
• Aged 18 years or older
• Pathologically confirmed invasive breast carcinoma
• A clinical T1-2 tumor
• Will be treated with lumpectomy and whole breast radiotherapy
• Clinically node negative status: no signs of axillary lymph node metastases at physical examination and preoperative axillary ultrasound (or negative cyto-/histopathology)
• Written informed consent

Exclusion Criteria:

• Clinically node positive pre-operative
• Bilateral breast cancer
• Evidence of metastatic disease
• History of invasive breast cancer
• Previous treatment of the axilla with surgery or radiotherapy (except surgery for hidradenitis suppurativa or for other superficially located skin lesions, such as naevi)
• Pregnant or nursing
• Other prior malignancies within the past 5 years (except successfully treated basal cell and squamous cell skin cancer, carcinoma in situ of the cervix or carcinoma in situ of the ipsilateral or contralateral breast) or unsuccessfully treated malignancies > 5 years before randomization
• Unable or unwilling to give informed consent