Since the introduction of sentinel node biopsy in breast cancer, it has become clear that its use is reliable and reproducible. Today, it is clinical routine to not remove further lymph nodes from the axilla (arm pit) in case the sentinel node (which is the first lymph node/s reached by lymphatic flow from the breast) is free of tumor deposits. It is also routine to leave remaining lymph nodes behind in case the sentinel node contains a minimal cluster of tumor cells, called isolated tumor cells (formerly submicrometastasis). Even in slightly larger tumor deposits, so called micrometastasis (up to 2 mm in size), it has been shown that a completion axillary clearance (removal of further lymph nodes from the arm pit) does not contribute to a better survival. Data from a randomized study indicate that it seems safe to omit axillary clearance even if the sentinel node biopsy shows up to 2 nodes with tumor deposits over 2 mm in size (macrometastasis). These studies have changed clinical practice in many countries, however, it is still debated whether it is safe to omit axillary clearance in the case of sentinel node macrometastasis due to under-recruitment in the aforementioned study. The rationale for omitting extensive axillary surgery is the avoidance of postoperative morbidity such as arm lymphedema, loss of sensation, pain and swelling.

The hypothesis is that refraining from axillary clearance in breast cancer patients with 1-2 sentinel nodes with macrometastasis will not worsen breast cancer-specific survival by more than a maximum of 2.5% after 5 years.

This study is a prospective international randomized trial including 3500 patients.

Breast cancer patients without signs of axillary nodal involvement will be eligible for sentinel node biopsy. Those who are found to have up to two sentinel node containing macrometastasis will be informed about this trial Those wishing to participate will be randomized to either undergo further axillary surgery (clearance) or not. Outcome measures are breast cancer-specific survival, disease-free survival, axillary recurrence rate and overall survival.

Details can be found on www.senomac.se

Inclusion Criteria:

• Patients with invasive breast cancer (T1-T3)
• N0 on palpation
• Preoperative ultrasound performed
• Pathology report shows macrometastasis in 1-2 sentinel lymph nodes
• Patients undergo breast-conserving therapy or mastectomy
• The patient must have provided oral and written consent
• Age ≥ 18 years

Exclusion Criteria:

• Metastases outside of the ipsilateral axilla
• Prior history of invasive breast cancer
• Pregnancy
• Bilateral breast cancer if one side meets exclusion criteria
• Medical contraindication for radiotherapy or systemic treatment
• Inability to absorb or understand the meaning of the study information; for example, through disability, inadequate language skills or dementia.