Accuracy of Intraoperative Sentinel Lymph Node Evaluation by Imprint Cytology in Breast Cancer: A 12-Year Single Center Experience With 2,528 Patients.

Objective: Sentinel lymph node biopsy (SLNB) is a key procedure for evaluating axillary lymph node status in early breast cancer, offering lower morbidity than axillary lymph node dissection. Intraoperative evaluation (IOE) of sentinel lymph nodes (SLNs) with methods like frozen section (FS) and imprint cytology (IC) aid in making immediate surgical decisions, although IOE accuracy may vary due to several factors. Materials and Methods: This retrospective study involved 2,528 patients with invasive breast cancer who underwent SLNB at a single institution from 2012 to 2024. Primarily, IC was used for intraoperative assessment, while FS was selectively performed in certain cases, such as with suspicious macroscopic findings or after neoadjuvant chemotherapy (NAC). The final diagnosis relied on permanent sections with serial step-leveling and classification of metastasis size. Results: IOE showed a sensitivity of 65.8% and specificity of 97% for detecting lymph node metastases. The combination of IC and FS yielded higher sensitivity (76.1%) compared to IC alone (64.1%), particularly for isolated tumor cells (ITC). Patients treated with NAC exhibited slightly lower IOE accuracy (83.8%) compared to those without NAC (85.9%). False negatives were more common in cases of micrometastasis, ITC, and invasive lobular subtype. Excluding micrometastasis and ITC significantly enhanced IOE accuracy. Conclusion: The accuracy of intraoperative SLN evaluation is affected by size of the metastasis, tumor subtype, and prior NAC. While IC is acceptable for IOE, combining IC and FS is advised, especially in the setting of earlier NAC, to enhance accuracy for small metastatic foci.