For HER2-low tumours which gave rise to HER2-negative recurrences, only one parameter was found to be different compared to tumours with a stable HER2 status (negative in the primary and in the recurrent tumour): a significantly higher Ki67 expression in the first tumour category (39.8 ± 20.2% versus 28.5 ± 17.1% for stable HER2-negative tumours; P = 0.037). Here, MKI67 is linked to neoplasm.