Abstract: Objective To assess the size and type of sentinel lymph node(SLN)metastases after neoadjuvant chemotherapy(NAC)for breast cancer using rapid immunohistochemistry(RD-IHC)technology, and to analyze the accuracy and false negative rate(FNR)of RD-IHC detection, as well as its correlation with clinical pathological characteristics. Methods The one-step RD-IHC method was used to detect the expression of CK(pan)in intraoperative frozen sections of SLNs after NAC for breast cancer. The detection rates(DR)of three methods-intraoperative hematoxylin and eosin(IH), RD-IHC, and routine hematoxylin and eosin(HE)plus immunohistochemistry(RHPI)-for SLN macro-metastases, micro-metastases, and isolated tumor cells(ITCs)were compared and analyzed, and the clinical pathological characteristics associated with FNR were further investigated. Results A total of 393 SLN biopsy specimens from patients undergoing NAC were collected, and 1,106 lymph nodes were detected, with an average of 1 to 5 SLN biopsies per case. IH detected 98 cases of SLN metastases, RD-IHC detected 123 cases, and RHPI detected 133 cases. Among them, the DR of IH for SLN micro-metastases and ITCs was 4.6% and 3.1%, respectively, with an FNR of 26.3%(35/133)and 22 delayed diagnoses, the DR of RD-IHC for SLN micro-metastases and ITCs was 8.8% and 6.2%, respectively, with an FNR of 7.5%(10/133)and no delayed diagnosis cases, the DR of RHPI for SLN micro-metastases and ITCs was 8.9% and 7.6%, respectively. Compared with IH, RD-IHC improved the DR of low-volume micro-metastases and reduced the FNR. In subgroup analysis, RD-IHC false negatives were mainly observed in cases with estrogen receptor(ER)-positive, progesterone receptor(PR)-positive, HER2-negative, P53 wild-type, and low Ki67 expression, and the FNR of SLN biopsy specimens containing micro-metastases was significantly higher than that of the macro-metastasis group. When the number of SLN biopsies per case reached more than 3, the DR of SLN biopsy significantly increased and the FNR decreased. Conclusion RD-IHC can significantly improve the intraoperative diagnostic accuracy of SLN metastasis after NAC in breast cancer within a short period of time, especially for cases with low-volume micro-metastasis. RD-IHC can effectively reduce the rate of delayed diagnosis and maintain the FNR within a controllable range, thereby avoiding unnecessary secondary surgery and effectively guiding the selection of clinical surgical methods.

Key words: Breast cancer, Sentinel lymph nodes, Neoadjuvant chemotherapy, Rapid immunohistochemistry