Would you continue her 2 neu directed therapy for a patient with breast cancer if a biopsy on progression confirms Her 2 neu negative disease?

There is no good evidence-based answer to this question even though biomarkers (ER, PR, HER2) can change over time (eg. from primary to metastatic recurrence, or pre and post neoadjuvant therapy) in 5-30% of cases.¹ There are no large series assessing outcomes based on changing or not changing thera...