ERBB2 and neoplasm: Indeed, we found a lower proportion of tumours expressing PR among patients for whom the HER2 status differed between the primary and the recurrent tumour (HER2-negative in the primary tumour and HER2-low in the recurrence), and— inversely—a higher proportion of PR-expressing primary tumours was found among patients with stable HER-negative status (69.6% versus 90.2%; P = 0.010).