ERBB2 and ductal breast carcinoma in situ: CISH is able to detect HER2 gene amplification and to minimise, if not eliminate, the borderline category with IHC.24 The performance of CISH in HER2 testing has rarely been tested in series, so we aimed to characterise HER2 status using IHC and CISH in DCIS and assess its prognostic value in a large and well annotated cohort.