ERBB2 and ductal breast carcinoma in situ: HER2 is an established negative prognostic factor in invasive breast cancer.11 The prognostic significance of HER2 status in DCIS is, however, less clear.1,12 The relationship of HER2 to risk of recurrence and its role in the progression from in situ to invasive cancer have been debated.9 HER2 over-expression is reported to be more frequent in DCIS than in invasive cancer.13 This may seem contradictory, as HER2 is proposed to play a role in tumour progression.