May axillary dissection be avoided after micro metastases in sentinel lymph node analyzed by OSNA method

18 Background: The study of the sentinel node biopsy is a common method to assess axillary involvement before surgical resection. The OSNA assay based on reverse transcriptase loop mediated amplification (RT-LAMP) and quantification of cytokeratin 19 (CK19) mRNA allows a rapid intra-operative detection of the metastases in the sentinel lymph node in breast cancer patients. Pathologists considered micro metastases when the size of the node involvement was between 0.2 and 2 mm and the OSNA method assess micro metastases when the copy number of CK19 is between 250 and 5000. Methods: From a total of 341 patients in which sentinel node had been analyzed, we studied a series of 32 patients whose sentinel nodes had micro metastases assessed by OSNA and who underwent subsequent axillary dissection. Median breast tumour size was 1.6 cm, 10 patients (31%) had less than 1 cm in size and only 6 patients (19%) had >2 cm. 78% of patients shown positive oestrogen receptor and 14 patients (44%) had low Ki67 (<14%). The C...