Background: Frozen section and intraoperative imprint cytology (IIC(N)) are 2 methods used for intraoperative pathologic assessment of sentinel lymph nodes (SLNs). The SLN evaluation of patients with invasive lobular carcinoma (ILC) results in a relatively high number of false-negative results using either of these methods. The purpose of this study was to evaluate the added benefits that intraoperative immunohistochemical-cytokeratin staining (I(CK-IHC)) can bring to IIC(N) in the evaluation of SLN in patients with ILC.
Methods: A total of 59 breast cancer patients with ILC underwent an SLN biopsy evaluated by our standard IIC(N) assessment in addition to I(CK-IHC). The results of IIC(N) with I(CK-IHC) were compared with the final histopathologic assessment consisting of standard hematoxylin and eosin staining and additional cytokeratin staining of nodes.
Results: Intraoperative evaluation of SLN using IIC(N) and I(CK-IHC) correctly diagnosed the nodal status in 45 of 59 (76.3%) patients. On final histopathologic assessment, 31 of 59 (52.5%) patients were found to have positive nodes. Using I(CK-IHC), 17 of these 31 positive cases (54.8%) were detected. Using IIC(N) alone, without the benefit of I(CK-IHC), only 13 of 31 (41.9%) positive cases were detected intraoperatively.
Conclusions: For patients with ILC, I(CK-IHC) staining in addition to IIC(N) improves accuracy over using IIC(N) alone. In this study, I(CK-IHC) staining demonstrated a 12.9% improvement in the detection of SLN metastases in patients with ILC. Cytopathologists should consider employing I(CK-IHC) staining to evaluate the touch-imprint slides of SLN in ILC patients.