61 Background: Recent trends in surgical practice advocate selective use of axillary nodal clearance (ANC) following sentinel lymph node biopsy (SNB) in the treatment of breast cancer. We aimed to determine the effectiveness of one-step nucleic acid amplification (OSNA) using CK19 mRNA copy number and tumor-related factors in predicting non-sentinel axillary nodal involvement, in order to formulate local guidelines for ANC. Methods: Patients due to have SNB at our institution for invasive breast cancer as well as selected patients with high grade ductal carcinoma in situ with negative assessment of the axilla on pre-operative imaging were included. Alternate slices of each node were sent for assessment by either OSNA or Histopathology. Immediate ANC was performed if OSNA was positive. The CK19 mRNA copy number, the total tumor load (summation of m RNA copy number of positive nodes,TTL), the total nodal status at ANC and tumor characteristics including grade, tumor size and lymphovascular invasion (LVI) for each patient were determined. A model of risk probability was constructed using TTL and tumor related factors. Results: 664 nodes were examined from 425 patients who had SNB performed between 2011 and 2014. After excluding 8 patients who did not meet the study criteria, 648 nodes from 417 patients were included for analysis. The concordance between OSNA and histology was 91.4%; positive predictive value (PPV) and negative predictive value (NPV) was 77% and 97% respectively. Patients with TTL less than 1400 did not have additional non sentinel lymph node involvement. TTL (p<0.01), and presence of LVI (p<0.05) were predictive for additional nodal involvement. The risk model identified all patients with more than 2 positive nodes as requiring ANC. All patients with non-sentinel node metastases at ANC were selected. Conclusions: OSNA is a sensitive and reliable intraoperative method for the detection of sentinel node metastases. Our study has shown it can also be used to predict the presence of non-sentinel metastases. Patients deemed high risk may be offered immediate ANC while axillary surgery in other groups may be omitted or be decision-based on risk stratification.
Intraoperative prediction of non‑sentinel lymph node metastases in breast cancer using cytokeratin 19 mRNA copy number: A retrospective analysis
