Accuracy of fine needle aspiration cytology (FNAC) of axillary lymph nodes as a triage test in breast cancer staging

Axillary node fine needle aspiration cytology (FNAC) has the potential to triage women with operable breast cancer to initial nodal surgical procedure. Because of variability in the reported accuracy of this test its role and clinical utility in pre-operative staging remains controversial.

We retrospectively evaluated the accuracy of ultrasound-guided axillary FNAC in all consecutive clinically T1-2 N0-1 breast cancers that had undergone this test (491 biopsies). We included subjects with clinically or sonographically indeterminate or suspicious nodes. Pathological node status was used as the reference standard (based on axillary dissection or sentinel node biopsy).

Sensitivity of node FNAC was 72.6% (67.3-77.9) and specificity was 95.7% (92.5-98.8) for all cases, sensitivity was lower at 64.6% (59.3-70.0) if inadequate cytology was included as a negative result. FNAC sensitivity was highest in women with clinically suspicious nodes [92.5% (88.2-96.7)] and lowest in women with sonographically abnormal and clinically negative nodes [50.0% (41.3-58.7)]. Specificity was high in both groups, 81.2% (54.5-96.0) and 97.2% (94.6-99.9), respectively. The false-negative rate was 15.3% (12.1-18.5), the false-positive rate was 1.4% (0.4-2.5), and the inadequacy rate was 10.8% (8.0-13.5). The likelihood of node FNAC being positive was significantly associated with tumour grade and stage, and the number of nodes involved with metastases.

Our data show that axillary FNAC has moderate sensitivity (which varies according to selection criteria for the test) and consistently high specificity, is associated with low inadequacy and very few false positives. We estimate that its use would have improved triage to initial nodal procedure in about one quarter of our cases. If one accepts the premise that initial surgical staging of the axilla should be based on all information available through pre-operative diagnosis, then axillary FNAC should be adopted routinely into clinical practice.