Abstract P2-01-28: Intraoperative assessment of the sentinel node (SN) in breast cancer by one step nucleic acid assay (OSNA): Experience of over 800 patients
Authors: Clarke D , Weston S , Ion C , Smith A , Kabir A , Harries S , Jones L 
Published: March 2017

Abstract
Introduction
The intra-operative assessment of the sentinel node in women with breast cancer enables an immediate axillary node clearance 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 which include: Touch Imprint Cytology, Frozen Section Analysis and Polymerase Chain Reaction (PCR) based molecular assays. OSNA is a molecular assay using 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 a single institution with 807 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 5 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 percentage 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
807 patients had their sentinel assessed intraoperatively using OSNA in this 5 year study period. The sentinel node was positive in 292 patients (36.5%). Of those who had a positive node, 138(17.3%) had macrometastatic disease and 154(19.2%) had micrometastatic disease. When compared to 411 patients in the preOSNA period, that were assessed by Touch Imprint Cytology and H&E sections, the node positivity rate increased from 24.6% to 36.5% (p 0.0001) with the introduction of OSNA. Whilst there was no significant increase in the rate of macrometastatic disease – 21.15% versus 17.3 %( p 0.052), there was a significant increase in the patients who had micrometastases detected on OSNA - 3.5% versus 19.2 %( p 0.0009) as shown in the table.
Comparison of OSNA with conventional Touch Imprint Cytology and H&EResult TIC and H&ETIC and H&EOSNAOSNAp value NumberPercentageNumberPercentage PositiveMacro8421.113817.30.052PositiveMicro143.515419.20.0009Negative 31365.451563.5
Conclusion
Our results prove that OSNA is a much more sensitive test for picking up metastatic disease, especially micrometastatic disease, in the sentinel node. Whilst this did cause some anxiety in the initial part of the study period, 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 always 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, Weston S, Ion C, Smith A, Kabir A, Harries S, Jones L. Intraoperative assessment of the sentinel node (SN) in breast cancer by one step nucleic acid assay (OSNA): Experience of over 800 patients [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-01-28.