While patients with stage I HER2-positive breast cancer were either excluded from or underrepresented in pivotal trials that established the survival benefits of trastuzumab in combination with poly-chemotherapy, retrospective data of untreated patients showed that even these small HER2-positive breast cancers have recurrence rates between 10–30%, justifying the need of adjuvant treatment in this context5–8. Here, ERBB2 is linked to breast carcinoma.