Reply: Isolated tumour cells and micrometastases in intraductal breast cancer: a simple mechanical question in some cases

The pathogenesis of lymph node metastases in preinvasive breast cancer – ductal carcinoma in situ (DCIS) – remains controversial. The one-step nucleic acid amplification (OSNA) assay is a novel molecular method that can assess a whole node and detect clinically relevant metastases. In this retrospective cohort study, we determined the performance of the OSNA assay in DCIS and the pathogenesis of node-positive DCIS.The subjects consisted of 623 patients with DCIS who underwent sentinel lymph node (SN) biopsy. Of these, 2-mm-sectioned nodes were examined using frozen-section (FS) histology in 338 patients between 2007 and 2009, while 285 underwent OSNA whole node assays between 2009 and 2011. The SN-positivity rate was compared between cohorts, and the characteristics of OSNA-positive DCIS were investigated.The OSNA detected more cases of SN metastases than FS histology (12 out of 285, 4.2% vs 1 out of 338, 0.3%). Most of the metastases were micrometastases. The characteristics of high-risk DCIS (i.e., mass formation, size, grade, and comedo) and preoperative breast biopsy (i.e., methods or time to surgery) were not valid for OSNA assay–positive DCIS.The OSNA detects more SN metastases in DCIS than FS histology. Further examination of the primary tumours and follow-up of node-positive DCIS are needed to elucidate the pathogenesis.