One Step Nucleic Acid Amplification (OSNA) positive micrometastases and additional histopathological NSLN metastases: Results from a single institution over 53 months

Abstract Introduction The role of sentinel lymph node micrometastases on histopathological analysis is controversial in axillary staging and management in clinically node negative breast cancer. Long-term studies addressing the clinical relevance of occult breast cancer in sentinel lymph nodes based on molecular analysis are lacking. One Step Nucleic Acid Amplification (OSNA), a highly sensitive assay of cytokeratin 19 mRNA, is used intra-operatively for the detection of lymph node macro- and micrometastases in breast cancer. Aim The aim of this study is to review the rate of micrometastases and further histopathological NSLN metastases, in our unit following the introduction of OSNA in Guildford. Methods Data was collected prospectively from the period of introduction 01/12/2008 to 31/05/2013. All patients eligible for sentinel lymph node biopsy were offered OSNA and operations were performed by the consultant breast surgeons. Presence or absence of micro-metastases depends on the agreed cut-off point on the amplification curve. On detection of micrometastases (+) and positive but inhibited (i+) metastases, a level 1 axillary clearance (ANC) was performed and for a macrometastasis (++), a level 3 ANC was carried out. Results 66% of the patients had negative SLN ( n = 672) and 34% ( n = 336) had positive sentinel lymph nodes who had further axillary surgery. Of these, 45% ( n = 152/336) had macrometastases, 40% ( n = 136/336) had micrometastases and 15% (48/336) had positive but inhibited results. There was no difference in the patient demographics and tumour characteristics in the various positive SLN groups. In patients with micrometastases, 15% (20/136) had further positive NLSNs and a further 6% (8/136) had >4 overall positive nodes (SLN + NSLN) thus requiring adjuvant supraclavicular/chest wall radiotherapy ( p