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.