A novel automated assay for the rapid identification of metastatic breast carcinoma in sentinel lymph nodes

Lymphatic mapping with the identification and removal of axillary sentinel lymph nodes (SLNs) currently is standard practice in the surgical management of patients with early stage breast cancer.1-3 SLNs are accurate predictors of the status of nonsentinel lymph nodes, with a negative predictive value (NPV) approaching 100%.4 Intraoperative evaluation of SLNs allows for complete axillary dissection at the time of primary breast surgery if the SLNs are identified as positive for metastatic tumor, eliminating the need for a second surgical procedure with its associated costs, morbidity, and patient distress. Although there is general agreement that SLNs should be sliced at 2-mm intervals for pathologic evaluation, to our knowledge, no consensus exists regarding the optimal method for intraoperative and final pathologic examination of SLNs in breast cancer. Intraoperative evaluation may include frozen section, touch imprint cytology (IC), scrape cytology, or a combination of these techniques. Although the specificity of these techniques is excellent, the sensitivity varies widely, ranging from 50% to 75%.5-8 It has been reported that intraoperative frozen section analysis of the entire lymph node sectioned at 50-μm intervals dramatically increases the sensitivity of detecting metastatic disease, although it is not feasible or practical at most centers.4 Intraoperative rapid cytokeratin immunostaining also can improve the sensitivity of the evaluation9; however, this test is not widely available. There also is much variability in the protocols adopted by different laboratories for the final pathologic evaluation of SLNs in breast cancer. In addition, pathologic assessments examine a very small amount of the lymphoid tissue and are subject to interobserver variability in interpretation,10 prompting the development of standardized techniques. Molecular testing of SLNs can enable standardized, objective, and rapid evaluation. In this report, we describe a novel, fully automated molecular device, the “One Step Nucleic Acid Amplification (OSNA) Breast Cancer System” (Sysmex Corporation, Kobe, Japan), which combines reverse transcription (RT) with isothermal loop-mediated DNA amplification (RT-LAMP) for the detection of cytokeratin 19 (CK19) messenger RNA (mRNA) as a marker of metastatic carcinoma in SLNs. In a large, prospective, multicenter study, we compared the performance of the OSNA system with that of a detailed histopathologic examination of the lymph node and with IC for the detection of metastatic carcinoma in axillary SLNs in patients who had early stage breast cancer.