Diagnostic value of intraoperative rapid cytokeratin immunostain in the cytological evaluation of sentinel lymph nodes in patients with invasive lobular carcinoma

Background: Sentinel lymph node (SLN) biopsy is the standard of practice in clinically node-negative patients with breast carcinoma. Intraoperative imprint cytology (IC) is often used in this setting. In cases of invasive lobular carcinoma (ILC), interpretation of IC slides may be challenging. Rapid cytokeratin immunohistochemistry (R-CK) has been used in this scenario. This study evaluated if the combination of IC and R-CK improves the sensitivity of intraoperative SLN evaluation of ILC in our setting. Methods: SLN of all cases of ILC in which IC and R-CK were performed in a 4 year period were included. Final tissue diagnosis was used as the gold standard. Results: Four hundred and twenty-seven of the 802 IC performed during the study period corresponded to paired IC and R-CK for ILC. Independently, IC and R-CK correctly classified the SLN as negative or positive in 355 cases (83%) and 324 (76%) cases, respectively. In combination, IC and R-CK correctly classified 304 (71%) of cases. R-CK failed in 56 cases. R-CK aided in rendering an accurate diagnosis in 59% of atypical cases (19/32). Patients with atypical IC and positive R-CK did not undergo axillary dissection. The addition of R-CK increased the turnaround time (TAT) by 24 minutes. Conclusions: In this study, the addition of R-CK did not improve the diagnostic accuracy in cases classified as negative or positive by IC, but resulted in a considerable increase in TAT. Although R-CK proved to be of diagnostic value in atypical IC cases, it did not appear to influence clinical management.