ERBB2 and breast carcinoma: Although the concordance rate between HER2 IHC and FISH is very high, a small percentage of patients had discordant results with negative HER2 IHC and positive HER2 FISH results: 1.5% positive HER2 FISH in patients with HER2 IHC score of 0, and 6.9% positive HER2 FISH in patients with HER2 IHC score of 1 in this study cohort of 4884 breast carcinomas.