P112. Clipped node pathology as a guide for limited axillary surgery in occult breast cancer

Introduction: Contemporary evidence-based management of patients with breast cancer and axillary lymph node metastases may involve omission of axillary lymph node dissection (ALND) in some situations, e.g., following neoadjuvant chemotherapy (NACT) when targeted axillary dissection (TAD) identifies no residual disease. In contrast, current guidelines continue to recommend ALND for patients with axillary metastases from occult breast cancer (OBC). These patients have limited representation in landmark studies of axillary surgery de-escalation.


Methods: Using data from a single-institutional observational cohort study, we evaluated the patient and tumor characteristics, regional staging, and surgical pathology for patients with OBC. We estimated the probability of pathologic complete response (pCR) stratified by receptor subtype, the diagnostic test characteristics of clipped node pathology for evaluating axillary nodal burden, and the outcomes of patients undergoing TAD.


Results: The cohort included 102 patients with OBC diagnosed between 2010 and 2025. 99 (97%) patients underwent MRI with no finding of a primary breast tumor. 53 (52.0%) patients had cN1, 16 (15.7%) cN2, and 33 (32.4%) cN3 disease. 37 (38.9%) patients had 1-3 abnormal LNs on ultrasound, 25 (26.3%) had 4-9, and 33 (34.7%) had more than 10. Of 96 patients who underwent surgery, most (88.5%) underwent NACT followed by ALND (87.5%). pCR occurred in 12 of 36 (33.3%) with hormone receptor-positive (HR+) HER2- disease, 11 of 12 (91.7%) with HR+HER2+ disease, 4 of 6 (66.7%) with HR-HER2+ disease, and 24 of 31 (77.4%) with HR-HER2- disease. Of 46 patients who underwent NACT and had pathology results for the index clipped axillary node, 33 (71.7%) had a negative clipped node. When the clipped node was negative, the probability of no positive ALNs was 93.9% (95% CI: 79.8-99.3%). When the clipped node was positive, the probability of additional positive ALNs was 69.2% (95% CI: 38.6-90.9%). Pathologic assessment of the clipped node alone would have resulted in a false negative rate of 13.3% (95% CI: 1.7-40.5%). The false negative rate in patients with cN1/2 disease was 0% (95% CI: 0-30.8%). At median follow-up of 4.2 years, there were no recurrences or deaths in the 7 patients who underwent TAD alone.


Conclusions: In patients with OBC, clipped index LN pathology is diagnostic of the disease burden in the remaining axillary LNs, suggesting that limited axillary surgery anchored in removal of the clipped node may allow for accurate axillary staging following systemic therapy.