Diagnostic accuracy and challenges of intraoperative frozen section evaluation for axillary sentinel lymph node biopsy and breast margins

Our study aims to audit and evaluate the accuracy and pitfalls of intraoperative evaluation of frozen sentinel lymph nodes (IOE-FSLN) and resection margins (IOE-FSM) compared to final findings in paraffin sections. A total of 264 cases underwent intraoperative evaluation, encompassing 688 sentinel lymph nodes (SLNs) and 1186 surgical margins. Frozen section (FS) diagnoses were compared with corresponding permanent sections of FS (PFS). Sensitivity, specificity, false-negative rate, false-positive rate, and concordance rates were assessed. Cases with discrepancies underwent a detailed histological review. The study predominantly comprised cases of invasive breast carcinoma (IBC) (74%). For FSLN reporting, sensitivity was 88.1%, specificity 100%, and FS-PFS concordance 99.0%. FSM reporting showed sensitivity of 85.0%, specificity 99.9%, and concordance 98.4%. Sampling errors accounted for 86% (FSLN) and 88% (FSM) of discrepancies, with interpretive errors present in 1/7 FSLN and in 2/17 FSM cases. The shave margin method demonstrated a higher false-negative rate in FSM reporting. The rate of final positive margins was reduced from 21.3% to 11.4% when IOE-FSM was utilized. IOE-FSLN and IOE-FSM showed high reliability in guiding intraoperative decisions for axillary lymph node dissection and achieving free surgical margins in one-stage surgeries. However, limitations include challenges in distinguishing metastatic carcinoma from benign mimics in FSLN and diagnosing certain features such as IBC with post-treatment changes, invasive lobular carcinoma in FSLN and FSM; IBC rich in tumour-infiltrating lymphocytes, low-grade (DCIS/IBC in FSM) without immunohistochemical studies.