Clinical Applicability of the WHO Reporting System for Axillary Lymph Node Fine-Needle Aspiration in Invasive Breast...

Axillary lymph node (ALN) fine-needle aspirations (FNAs) can guide the next steps in the management of patients with invasive breast carcinoma (BC). The objective is to evaluate the diagnostic performance of ALN FNA in the detection of metastatic breast carcinoma.

We evaluated ALN FNAs from 2020 to 2024 to determine the risk of malignancy (ROM) of different cytologic diagnostic categories using a general WHO cytology reporting system framework (insufficient, benign, atypical, suspicious, and malignant).

A total of 290 axillary lymph node FNAs from patients with newly diagnosed invasive breast carcinoma were identified, of which 226 (78%) had histologic and/or adequate clinical follow-up. Cytologic diagnoses included six (2.1%) non-diagnostic, 99 (34.1%) benign, two (0.7%) atypical, seven (2.4%) suspicious for malignancy, and 176 (60.7%) malignant cases. The risk of malignancy (ROM) was 50.0% for non-diagnostic, 17.0% for benign, 100% for atypical, 85.7% for suspicious, and 99.2% for malignant diagnoses. Most false-negative benign cases were attributed to sampling limitations rather than interpretive error, with five cases showing only a single sentinel lymph node metastasis measuring <5 mm. Indeterminate diagnoses were most commonly associated with scant cellularity, acellular cell blocks, obscuring blood or fibrin, and equivocal immunohistochemistry. Excluding cases without histologic follow-up, ALN FNA demonstrated a sensitivity of 86.5%, specificity of 97.4%, positive predictive value of 98.5%, negative predictive value of 79.2%, and overall accuracy of 90.3% for the detection of metastatic breast carcinoma (OR = 243.2, Fisher's exact test, p < 0.0001).

ALN FNA is a highly reliable method for confirming axillary lymph node metastasis in invasive breast carcinoma when malignant cells are identified, with a ROM of 99% for the malignant category. The suspicious category was also strongly associated with malignancy (ROM 86%). However, the 17% ROM observed in the benign category indicates that a negative FNA does not reliably exclude metastatic disease, and surgical nodal staging may still be warranted in clinically or radiologically suspicious cases. These findings support the clinical applicability of the WHO System for Reporting Lymph Node Cytopathology and provide breast carcinoma-specific ROM estimates for this clinical setting.