Objective To compare the differences between 2013 and 2018 ASCO/CAP HER2 testing guidelines in 568 immunohistochemical HER2 equivocal breast cancer patients and to analyze the accuracy and deficiency of dual-color silver enhanced in-situ hybridization (DISH) by comparing with FISH.

Methods We selected 568 cases of paraffin-embedded invasive breast cancer specimen which were proved as HER2 equivocal by immunohistochemical (IHC). The HER2 gene amplification status was evaluated by FISH and comparatively analyzed according to both the 2013 and 2018 ASCO/CAP HER2 Testing guidelines respectively. Sixty specimens were randomly selected for DISH detection and compared with FISH.

Results According to the 2013 guideline, the number of HER2 positive, negative and equivocal cases were 183 (32.22%), 365 (64.26%) and 20 (53.52%), respectively. Compared with the 2013 guideline, HER2 positive rate decreased by 4.58% according to the revised 2018 guideline, and the negative rates were same; the difference of positive rates was statistically significant (P < 0.01). Comparison between FISH and DISH findings in 60 samples, the total, positive and negative coincidence rates were 95.0%, 94.7% and 100%, and the results of the two methods are significantly correlated (r=0.636, P < 0.01).

Conclusion Compared with 2013 ASCO/CAP guideline, the revised 2018 guidelines is more accurate and instructive for clinical medication. DISH could achieve similar precise results as compared to FISH. Bright field detection is the irreplaceable advantage of DISH.