Anticipating changes in the HER2 status of breast tumours with disease progression-towards better treatment decisions in the new era of HER2-low breast cancers.

HER2 status changes with BC progression, with enrichment of HER2-low tumours in advanced stages. The ER+/PR- status, low proliferation index and time to late recurrence correlated with these changes. These findings highlight the need of retesting recurrences, especially of HR + primary tumours, to identify candidates for new anti-HER2 therapies.