Impact of Histological Type and Grade on the Diagnostic Accuracy of Intraoperative Frozen Section for Detecting Breast Cancer Metastasis to Axillary Sentinel Lymph Nodes

Introduction Intraoperative sentinel lymph node (SLN) evaluation is the standard of care in patients with clinically node-negative breast cancer. The most common histological subtype of breast carcinoma is invasive ductal carcinoma (IDC), followed by invasive lobular carcinoma (ILC). Alternatively, histological grades vary from grades G1 to G3. Therefore, in this study, we evaluated the diagnostic accuracy of frozen section (FS) for detecting breast cancer metastasis to SLNs with respect to histological subtypes and grades. Methods A retrospective observational study was conducted in the Department of Histopathology at Liaquat National Hospital and Medical College, Pakistan, from January 2013 till December 2020, over a duration of eight years. A total of 540 cases of primary breast cancer, undergoing upfront breast surgery were included in the study. Intraoperatively, SLNs were identified and sent for FS. After FS reporting, the remaining tissue was submitted for final (paraffin) section examination after formalin fixation, and results of FS and final (paraffin) sections were compared. Results The mean age of the patients included in the study was 52.05±12.42 years, and the median number of SLNs was three (ranging from one to 14). The overall sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of intraoperative FS were 88.2%, 100%, 100%, 92.5%, and 95.2%, respectively. The sensitivity of FS for IDC was 88.3%, whereas it was 85.7% for ILC. Alternatively, the sensitivity of FS for grade G1, G2, and G3 tumors was 78.3%, 91.5%, and 90.2%, respectively. The false-negative rate for grade G1 tumors was 21.7%, which was higher than G2 and G3 tumors (8.5% and 9.8%, respectively). Similarly, the false-negative rate for cases where the number of SLNs was more than three was only 5.4%, which was lower than cases with a single and two to three SLNs sent on FS (23.1 and 14.7%, respectively). Conclusion The sensitivity of intraoperative FS for detecting ILC metastasis to axillary SLNs was not substantially different from IDC; however, histological grade affects the sensitivity of FS diagnosis, with lower-grade tumors having low sensitivity. Moreover, increasing the number of SLNs sent intraoperatively on FS improves the sensitivity of FS for detecting breast cancer metastasis to axillary SLNs.