ERBB2 and neoplasm: Indeed, for patients who presented with distant metastases, HER2-negative tumours which relapsed as HER2-low more frequently expressed ER (94.8% versus 73.0% among tumours which relapsed without a change in the HER2 status; P = 0.001), had significantly lower proliferation indexes (3.1 ± 3.6/mm2 versus 7.3 ± 9.6; P = 0.008) with lower mitosis scores (56.1% versus 35.6% with mitosis score I; P = 0.020) and lower Ki67 expression (28.7 ± 19.6% versus 32.8 ± 22.9%; P = 0.047).