MKI67 and neoplasm: For tumor stage 1 to 2, nodal stage 0 to 1, ER+/HER2− breast cancer, the International Ki-67 in Breast Cancer Working Group’s (IKWG) consensus in 2021 recommended using Ki-67 to aid in the decision-making of adjuvant chemotherapy only for cases with a very low (< 5%) or very high (> 30%) PI due to substantial inter-rater variability within this range8,9.