ERBB2 and cancer: Aside from younger age, further indications for a subsequent tumor bed boost are well summarized in diverse guidelines [4,5,6,7] and include: tumor grade 3, tumor size >2 cm, biological cancer subtypes at higher-risk (e.g., triple negativity or positivity for Her2-neu), predominant ductal carcinoma in situ (DCIS) components, and R1-status.