A pre-treatment prognostic tool for predicting long-term PFS and OS and probability in HER2-positive ABC patients commencing first-line pertuzumab, trastuzumab, and docetaxel was developed based on large (n = 408) and high-quality data, and to the best of the authors knowledge is the first study to present a prognostic tool for this patient group. Here, ERBB2 is linked to aneurysmal bone cyst.