For breast cancer patients with a metastatic sentinel node (SN), axillary dissection (AD) has been standard treatment. However, for patients with minimal SN involvement, AD may be overtreatment. IBCSG Trial 23-01 was designed to determine whether no AD is non-inferior to AD in patients with one or more micrometastatic (≤2 mm) SNs and tumour ≤5 cm.

In this multicentre trial patients were randomised to AD or no AD. Eligibility was limited to patients with clinically-palpable axillary lymph node(s) and a primary tumour ≤ 5 cm who, after sentinel node biopsy, had one or more micrometastatic (≤ 2 mm) sentinel lymphs nodes with no extracapsular extension. The primary endpoint was disease-free survival (DFS). Non-inferiority was defined as a hazard ratio of <1·25 for no AD vs. AD. The analysis was intention to treat. Patients were randomly allocated in a 1:1 ratio to AD or no AD with stratification by centre and menopausal status. There was no attempt to blind the treatment assignment. The trial is registered with ClinicalTrials.gov, NCT00072293. Per protocol, disease and survival information continues to be collected yearly.

From 2001 to 2010, 934 patients were randomised; 931 were evaluable (464 in the AD group and 467 in the no AD group). After a median follow-up of 5·0 (IQR 3.6–7.3) years, there were 124 DFS events, including breast-cancer-related events in 95 patients (local, 18; contralateral breast, 12; regional, 6; and distant, 59), and other events in 29 (second malignancy, 26; death without prior cancer event, 3). Five-year DFS was 87·8% (95% CI 84·4%–91·2%) in the no AD group and 84·4% (95% CI 80·7%–88·1%) in the AD group (log-rank p=0·16) (HR no AD vs. AD=0·78, 95% CI 0·55–1·11, non-inferiority p=0·0042). Patients with reported long-term surgical events (grade 3–4) included 1 sensory neuropathy (grade 3), 3 lymphedema (2 grade 3 and 1 grade 4), and 3 motor neuropathy (grade 3), all in the AD group, and 1 grade 3 motor neuropathy in the no AD group. One serious adverse event was reported, a post-operative infection in the axilla in the AD group.

AD in patients with early breast cancer represented in this study (most had tumours < 3 cm (92%; 856/931), received breast conserving surgery (91%; 845/931) and adjuvant systemic therapy (96%; 892/931)) should be avoided when the SN is minimally involved, thus eliminating complications of axillary surgery with no adverse effect on survival.

Supported in part: local participating centres, IBCSG central funds, CA075362 from the U.S. National Cancer Institute, and Swiss Cancer League/Cancer Research- Switzerland/Oncosuisse (ICPOCS 01688-03-2005). No pharmaceutical company funds were used.