ERBB2 and breast cancer: HER2 double-equivocal (IHC2+ and FISH group 4) cases were classified as HER2 negative according to the 2018 ASCO/CAP guidelines of HER2 testing in breast cancer, so only 1.3% HER2 positive patients (19) were determined in the HER2 negative population (1533-22) by additional FISH test using another block from the same tumor.