Abstract P3-03-11: Intraoperative assessment of the sentinel node in breast cancer by one step nucleic acid assay: Experience of over 1100 patients

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Abstract Introduction The intraoperative assessment of the sentinel node in women with breast cancer enables an immediate axillary node clearance to be done as part of the same operative procedure if the sentinel node is positive. This has significant benefits for the Patient, the Surgeon and the Health Care Provider. There are a variety of methods for the intra-operative assessment of the sentinel node which include: Touch Imprint Cytology, Frozen Section Analysis and Polymerase Chain Reaction (PCR) based molecular assays. OSNA is an automated molecular assay using a Polymerase Chain Reaction (PCR), which detects the presence of cytokeratin 19 in the sentinel node. We report our experience of OSNA for the intraoperative assessment of the sentinel node in our institution with 1148 patients. Methods All patients with operable breast cancer who were found to be node negative on clinical and radiological assessment of the axilla, and who had their axilla staged by a sentinel node biopsy at the Breast Unit at Warwick Hospital, UK over a 7 year period were included in this study. Data was collected from a prospective database maintained at the Breast Unit. The axillary node positivity rate and the number of patients with macrometastatic and micrometastatic disease as detected by OSNA was collected and compared with a group of 411 patients who had the intraoperative assessment by Touch Imprint Cytology and final histology by conventional Haematoxylin & Eosin (H&E) assessment, prior to the introduction of OSNA. The Chi-square test were used for statistical significance. Results 1148 patients had their sentinel node assessed intraoperatively using OSNA in this 7 year study period. The sentinel node was positive in 376 patients (32.8%). Of those who had a positive node, 183 (15.9%) had macro-metastatic disease and 193 (16.8%) had micro-metastatic disease. When compared to 411 patients in the pre-OSNA period, that were assessed by Touch Imprint Cytology and H&E sections, the node positivity rate increased from 23.8% to 32.8% (p<0.05) with the introduction of OSNA. Whilst there was no significant increase in the rate of macrometastatic disease – 20.4% versus 15.9 % ( p0.038), there was a significant increase in the patients who had micrometastases detected on OSNA - 3.4% versus 16.8 % ( p<0.05) as shown in the table. Conclusion Our results demonstrate that OSNA is a more sensitive test for picking up metastatic disease, especially micrometastatic disease, in the sentinel node. Whilst this did cause some anxiety initially, the results of recent trials like ACSOG Z-11 and IBCSG 23-01 have shown that small volume disease or micrometastases in the sentinel node do not require an axillary node clearance. Intraoperative assessment of the sentinel node with OSNA significantly upstages the axillary nodal status, especially with regard to micrometastatic disease, but the ability to proceed to an axillary node clearance at the same operation as the sentinel node biopsy, still has significant advantages for the Patient, Surgeon and Health Care Providers. Citation Format: Clarke D, Sinha A, Ion L, Weston S, Jones L, Kham M, Harries S. Intraoperative assessment of the sentinel node in breast cancer by one step nucleic acid assay: Experience of over 1100 patients [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-03-11.