Intraoperative Imprint Cytologic Evaluation of Sentinel Lymph Nodes for Lobular Carcinoma of the Breast

Background: The evaluation of sentinel lymph nodes (SLNs) from a woman with lobular cancer of the breast is frequently challenging. Intraoperative imprint cytology (IIC) is equivalent to frozen sectioning for rapid SLN evaluation and is advantageous because it is rapid, reliable, cost-effective, and conserves tissue. Metastatic lobular carcinoma is difficult to identify in SLN because of its low-grade cytomorphology, its tendency to infiltrate lymph nodes in a single cell pattern, and because individual cells can resemble lymphocytes. We are unaware of any large published studies, using any technique, to evaluate SLN for lobular carcinoma. Methods: A retrospective review of the intraoperative imprint cytology results of 678 SLN mapping procedures for breast carcinoma was performed. From this cohort, we studied SLN from cases of lobular carcinoma. These SLN were evaluated intraoperatively by either bisecting or slicing the SLN into 4-mm sections. Imprints were made of each cut surface and stained with hematoxylin and eosin and/or Diff-Quik. Permanent sections were evaluated with up to 4 hematoxylin and eosin-stained levels and cytokeratin immunohistochemistry. IIC results were compared with final histologic results. Results: Sixty-one cases of pure invasive lobular carcinoma were identified. Sensitivity was 52%, specificity was 100%, accuracy was 82%, negative predictive value was 78%. No statistically significant differences in sensitivity, specificity or accuracy were identified for the intraoperative detection of lobular carcinoma versus ductal carcinoma. The sensitivity for detecting macrometastases (more than 2 mm) was better than for detecting micrometastases, 73 versus 25%, respectively (P = 0.059). Conclusions: The sensitivity and specificity of IIC are similar to that of intraoperative frozen section evaluation. Therefore, IIC is a viable alternative to frozen sectioning when intraoperative evaluation is required. If SLN micrometastasis is used to determine the need for further lymphadenectomy, more sensitive intraoperative methods will be needed to avoid a second operation.