OPBC-07/microNAC study: Oncological outcomes with and without axillary lymph node dissection in patients with residual micrometastases after neoadjuvant chemotherapy

The OPBC-07/microNAC international (84 centres across 30 countries) retrospective (2013-2023) cohort study evaluated short-term oncological outcomes in patients with residual axillary micrometastasis (ypN1mi) after neoadjuvant chemotherapy in cT1-4, cN0-3 disease. All patients underwent either sentinel lymph node biopsy, targeted axillary dissection, or marked lymph node biopsy as a primary staging procedure. Completion ALND was performed in 50.7% (n=804), and regional nodal irradiation was delivered in 79.9% (n=1267) of patients. The primary endpoint was 3-year axillary recurrence, and secondary endpoints included any invasive recurrence. 

Of the 1585 patients included, 66.5% (n=1054) were node-positive at diagnosis. Subtypes were ER+/HER2- in 51.0% (n=808), HER2+ in 31.1% (n=493) and TNBC in 17.9% (n=284). After a median of 3.1 years of follow-up, any axillary recurrence occurred in 2.1% (n=34), and there was no difference between completion ALND and its omission (1.7% [95% CI, 0.9–2.9] versus 2.3% [1.4–3.7]; p=0.92). Nevertheless, omission of regional nodal irradiation was associated with increased axillary recurrence in adjusted analyses.

In an exploratory analysis of TNBC, completion ALND was associated with lower rates of axillary recurrence (2.4% [95% CI, 0.7–6.5] versus 8.7% [4.4–15.0]; p=0.018); however, no association with any invasive recurrence was found. 

These observational data document an increasing practice of axillary de-escalation, and ALND may not be necessary in patients with residual micrometastases after neoadjuvant chemotherapy. Prospective long-term data are needed to account for contemporary neo/adjuvant systemic regimens (e.g. immune checkpoint inhibitors for TNBC and CDK4/6 inhibitors for ER+ tumours).

Summary authors: Mr James Lucocq, Registrar, Western General Hospital, Edinburgh; Mr Amit Agrawal, Consultant Breast Surgeon and Associate Professor affiliated with Cambridge University Hospitals.