Objective: To determine the diagnostic accuracy of ultrasound guided fine needle aspiration (FNA) cytology and core needle biopsy (CNB) of axillary lymph nodes pre-operatively in newly diagnosed operable primary breast cancer.

Methods: An observational study for all patients who underwent pre-operative FNA cytology or CNB during September 2013–August 2014 was conducted at our institution (County Hospital, Stafford, UK). The accuracy of pre-operative axillary staging was compared to the postoperative histology. For this sensitivity, specificity, positive predictive value (PPV) and negative predictive values (NPV) were calculated.

Results: A total of 81 consecutive patients were evaluated by axillary ultrasound. Patients identified with potentially abnormal axillary lymph nodes underwent definitive surgery. Seven patients had positive cytology/histology who did not undergo definitive surgery and were excluded (N = 74) from the study. CNB had a sensitivity of 100% versus 72% (p = 0.006) for FNA cytology. Both had 100% specificity and PPV. The NPV of CNB was 100% versus 72% for FNA cytology. Among 35% of patients that underwent FNA cytology required repeat procedure versus 2.6% of patients who underwent CNB. 0/38 patients that had CNB required a second operation while 7/43 patients with negative FNA cytology had positive lymph nodes identified at sentinel lymph node biopsy (SLNB) requiring surgical re-intervention with axillary node clearance.

Conclusion: CNB was superior to FNA cytology when interrogating the axilla. We recommend CNB to be adopted routinely in pre-operative axillary staging to reduce surgical re-intervention.