Abstract P1-01-10: Comparison of sentinel lymph node positivity rates pre and post introduction of OSNA molecular analysis

Abstract

Abstract Introduction: Intra-operative assessment (IOA) of the axillary sentinel lymph node (SLN) allows immediate completion axillary lymph node dissection (cALND) for a positive SLN. One-step nucleic acid amplification assay (OSNA, (Sysmex)), a molecular technique, is very sensitive and may upstage the axilla compared with other forms of intra-operative assessment and with formal, paraffin-embedded haematoxylin and eosin (H&E) histopathology. This would result in an increased cALND rate at a time when efforts are being made to reduce unnecessary axillary surgery in line with the Z0011 trial (Giuliano et al. 2011). This study compares node positive rates before and after two changes in practice: the introduction of OSNA and the unit policy to perform cALND for macrometastatic SLN disease only. Methods: All patients in our unit undergo pre-operative axillary ultrasound with fine needle aspiration cytology of any suspicious nodes. Those with malignant cytology proceed directly to ALND. Radiologically and cytologically node negative patients undergo SLNB. Consecutive electronic records were examined for all SLNB procedures in two groups: Pre-OSNA from June 2006 to December 2010 and OSNA from August 2011 to March 2012. Pre-OSNA, patients were offered cALND for micro-or macroscopic SLN disease identified by H&E histology. Following Z0011, patients in the OSNA group proceeded to cALND for SLN macrometastases but not for micrometastases. The chi-squared test was used to compare results between the two groups. Results: The groups were similar in terms of age, tumour size, grade and receptor status. Sentinel node and cALND results are shown in table 1. In summary, testing by OSNA resulted in a higher node positive rate and a greater proportion reported with micrometastases (40% compared with 23% pre-OSNA). The OSNA macrometastasis rate was equal to the pre-OSNA overall node positive rate (22%). Among patients proceeding to cALND (all node-positive pre-OSNA patients and OSNA patients with macrometastases) there was no significant difference in the proportion with additional positive nodes in the cALND or the proportion with a total of four or more positive nodes. Conclusion: The introduction of OSNA has increased the proportion of patients identified as node positive, and has increased the proportion reported to have macrometastasis. Simultaneously, the decision not to perform cALND for patients with micrometastasis was intended to limit the additional surgery performed in the SLNB group as a whole. However, since this decision was based on data from studies using H&E assessment, we should look for ways to raise the threshold for cALND such that it includes only the patients at the highest risk of axillary recurrence. Reference Giuliano AE et al. JAMA 2011; 305(6): 569–75. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-01-10.