MKI67 and neoplasm: Thus, the tumours of younger women were more frequently estrogen receptor (ER)/progesterone receptor (PgR)-negative (χ2 = 7.07; P = .008), HER2 amplified (χ2 = 5.76; P = .01), and with high (≥10%) Ki67 labelling index (χ2 = 9.53; P = .002).