One-step nucleic acid amplification (OSNA) is a novel method introduced for the lymph node staging of breast cancer and has been tested in multiple series. The present review summarises current literature and concerns related to the new method. The results of this automated molecular assay based on the quantification of cytokeratin 19 mRNA show a 96% concordance rate with detailed histopathology complemented with immunohistochemistry when alternative slices of the same lymph node are used for the two tests. The low false-negative rate makes OSNA suitable for the intraoperative evaluation of sentinel lymph nodes. The false-positive rate also seems very low. Most discordant cases are explainable by low volume metastases (micrometastases), which may be missing from the material submitted for one test, but not from the different part used for the other test. It is tempting to change the gold standard for comparisons between the methods, and if this is done, histology seems to come out as a weaker test for the identification of metastases. OSNA detects more low volume nodal involvement, but it is uncertain whether these require further axillary treatment, and this will be a subject for future investigations. Therefore, it is also uncertain whether the advantage of OSNA of detecting practically all metastases due to complete sampling of lymph node tissue is clinically more important than the exclusion of metastases greater than micrometastasis that can be reliably done by intraoperative microscopy followed by permanent section histology.
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Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.
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