ERBB2 and neoplasm: When focusing on patients with HR-positive primary tumours, i.e., the population for which the HER2 status changes were the most frequent, we found that the time to recurrence was also—as for the whole study population—the main factor associated with these changes, both for the whole group with HR-positive primary tumours and just those with HR-positive local recurrences (P = 0.014 and P = 0.006, respectively), and this was independent of the primary tumour HR status at diagnosis.