ESR1 and breast carcinoma: The International Ki67 Working Group, or IKWG, suggested that “In this T1-2, N0-1 patient group, the IKWG consensus is that Ki67 5% or less, or 30% or more, can be used to estimate prognosis” for identifying estrogen receptor (ER) positive and Her2 negative breast cancer patients who may not need adjuvant chemotherapy (2).