Intraoperative evaluation of sentinel lymph nodes for metastatic breast carcinoma by imprint cytology

Background: The increasing utilization of lymphatic mapping techniques for breast carcinoma has made intraoperative evaluation of sentinel lymph nodes attractive. Axillary lymph node dissection can be performed during the initial surgery if the sentinel lymph node is positive, potentially avoiding a second operative procedure. At present the optimal technique for rapid sentinel lymph node assessment has not been determined. Both frozen sectioning and intraoperative imprint cytology are used for rapid intraoperative sentinel lymph node evaluation at many institutions. The purpose of this study is to evaluate experience with imprint cytology for intraoperative evaluation of sentinel lymph nodes in patients with breast cancer. Methods: A retrospective review of the intraoperative imprint cytology results of 678 sentinel lymph node mappings for breast carcinoma was performed. Sentinel nodes were evaluated intraoperatively by either bisecting or slicing the sentinel node into 4 mm sections. Imprints were made of each cut surface and stained with H&E and/or Diff-Quik. Permanent sections were evaluated with up to four H&E stained levels and cytokeratin immunohistochemistry. Intraoperative imprint cytology results were compared with final histologic results. Results: The sensitivity of imprint cytology was 53%, specificity was 98%, positive predictive value was 94%, negative predictive value was 82% and accuracy was 84%. The sensitivity for detecting macrometastases (more than 2mm) was significantly better than for detecting micrometastases (≤2 mm), 81 versus 21%, respectively (P < 00001). Conclusions: The sensitivity and specificity of imprint cytology are similar to that of intraoperative frozen section evaluation. Imprint cytology is therefore a viable alternative to frozen sectioning when intraoperative evaluation is required. If sentinel lymph node micrometastasis is used to determine the need for further lymphadenectomy, more sensitive intraoperative methods will be needed to avoid a second operation.