[Impact and clinical value of the revised 2019 Chinese HER-2 testing guidelines on the detect result evaluation of invasive breast cancer cases with equivocal HER-2 immunostaining by using fluorescence in situ hybridization].

Objective: To investigate the impact and clinical significance of the revised 2019 Chinese HER-2 testing guidelines on the detecting result evaluation of invasive breast cancers with equivocal HER-2 immunostaining by using fluorescence in situ hybridization (FISH). Methods: A total of 569 cases of invasive breast cancers with HER-2 (+ + ) immunostaining evaluated according to the immunohistochemistry (IHC) guidelines of 2014 edition and 2019 edition from May to November 2019 were collected and further detected by FISH. The results of HER-2/CEPl7 double probe were respectively interpreted according to both the 2014 and 2019 Chinese HER-2 testing guidelines and the results were compared. Results: According to the 2014 guidelines, the number of HER-2 positive, equivocal and negative cases were 139 (24.43%), 67 (11.78%), and 363 (63.80%), respectively. Whereas according to the 2019 guidelines, 115 cases (20.21%) were the first group, 9 cases (1.58%) were the second group, 15 cases (2.64%) were the third group, 67 cases (11.78%) were the fourth group, and 363 cases were (63.80%) the fifth group, of which 130 cases (22.85%) were positive and 439 cases (77.15%) were negative by FISH detecting. Compared with the guideline of 2014 edition, the HER-2 positive rate of FISH detection reduced from 24.43% (139/569) to 22.85% (130/559) according to the application of the guideline of 2019 edition, but the difference was not statistically significant (P=0.567), while the negative rate increased from 63.80% (363/569) to 77.15% (439/569), with a statistically significant difference (P<0.05). Forty-three cases with incomplete weak to medium intensity of IHC membrane staining which were HER-2 (+ + ) according to 2014 guideline were changed to IHC (+ ) on the basis of the 2019 guideline. According to the FISH guideline of 2014 edition, 1 case (2.33%) was positive, 6 cases (13.95%) was equivocal and 36 cases (83.72%) was negative, while according to the 2019 FISH guideline, all of the 43 cases were negative. Conclusions: According to the guideline of 2019 edition, a proportion of cases changes from HER-2 (+ + ) to (+ ), and the HER-2 positive rate of FISH test decreases slightly, the negative rate increases, the equivocal result is eliminated, which provides a definite reference for screening patients who will be benefited from the targeted treatment of HER-2.