Abstract P1-01-11: Is OSNA mRNA copy number in sentinel lymph node biopsy predictive of further disease in the axilla?
Authors: Rusby JE , Agabiti E , Waheed S , Barry P , Roche N , Allum W , Gui G , MacNeill F , Christaki G , Osin P , Nerurkar A 
Published: August 2014

Abstract
Introduction: Intra-operative assessment of sentinel nodes (SLNs) allows immediate completion axillary dissection (cALND) in breast cancer patients. Molecular assessment such as one-step nucleic acid amplication (OSNA) promises greater sensitivity and provides a more accurate quantitative assessment than traditional methods.
Our unit policy is to proceed to cALND in patients with macrometastases but not for micrometastases. However, evidence of upstaging has led us to seek to raise the threshold for proceeding to cALND. The CK19 mRNA copy number is an expression of the metastatic burden in the SLN and may be related to the presence of additional disease in the cALND. Since the original copy number threshold between micro (250–5000 copies/microliter) and macrometastasis (&gt;5000 copies/microliter) was based on few patients and serial pathological sections, we investigated the mRNA copy number in patients with and without additional disease in the cALND.
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 sentinel lymph node biopsy (SLNB) and OSNA. Electronic records of consecutive patients with invasive breast cancer undergoing SLNB with OSNA from August 2011 to March 2012 were retrospectively reviewed. Two parameters of mRNA copy number were examined: Copy number of the highest copy number SLN and the summed copy numbers of all positive SLNs. Their relationship to the presence of further disease in the axilla was examined using Student's t test.
Results: Of 201 SLNBs, 45 (22%) had macrometastasis-positive OSNA and therefore underwent cALND (1 patient declined). Twenty patients (45%) had no further positive nodes (a negative cALND) with a total axillary metastatic burden of 1–2 in 11–27 nodes. Twenty four (55%) showed further disease (a positive cALND) with a burden of 2–20 in 9–30 nodes, including the SLNs.
There was no significant difference in tumour size or grade between patients with additional positive nodes in the cALND compared with those with no further disease.
There was no significant difference in the copy number of the highest copy number positive SLN (p = 0.44) or in the summed copy number of all positive SLNs (p = 0.36) between the cALND positive and negative groups.
Conclusion: OSNA CK19 mRNA copy number does not correlate with the cALND metastatic burden. Therefore, raising the copy number threshold may be too simplistic as a method to better select patients with high probability of a positive cALND. A predictive model will be derived based on multivariate analysis of the larger patient population (&gt;400 patients) that will have undergone SLNB with OSNA by the time of SABCS.
Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-01-11.