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[Reevaluation of equivocal HER2 status detected by immunohistochemistry according to the 2019 guidelines for HER2 detection].

Objective To understand the effects and clinical significance of the 2019 guidelines for the human epidermal growth factor receptor 2 (HER2) detection. Methods: According to the 2014 guidelines, 548 cases of invasive breast cancer with equivocal HER2 (2+) detected by immunohistochemistry (IHC) in Taizhou Enze Medical Center, Zhejiang Province, China from 2013 to 2019 were selected. The results of IHC and HER2/CEPl7 double-probe were reevaluated and divided into groups according to the 2019 guidelines for the comparative analysis. Results: Among the 548 IHC HER2 (2+) invasive breast cancers, the number of positive, equivocal and negative cases for HER2 were 96 (17.52%), 81 (14.78%) and 371 (67.70%), respectively, according to the 2014 guidelines. However, according to the 2019 guidelines, 10 cases (1.82%) were reclassified as IHC 1+, 2 cases in the group 2 were reclassified as negative, and all the originally equivocal cases in group 4 were reclassified as negative. Finally, the total number of positive and negative cases for HER2 were 94 (17.15%) and 454 (82.85%), respectively. Conclusions: After applying the 2019 guidelines, the number of IHC 2+ cases decreases, and the positive rate for HER2 also decreases slightly due to the reevaluation change in groups 2 and 4, leading to reclassification of the cases that were deemed equivocal according to the 2014 guidelines. In general, the new 2019 guidelines are more reasonable and easier to use.