ERBB2 and breast carcinoma: Among 4884 breast carcinomas that had concurrent HER2 IHC and HER2 FISH, over one-fifth of cases (n = 1059, 21.7%) had a negative HER2 IHC result (IHC score of 0 and 1 +) and approximate three-fourth of cases (n = 3563, 73.0%) had an equivocal IHC result (IHC score of 2 +) (Fig. 1).