Ki67 positivity 20% prognosis needs to be judged in relation to the boundaries of different tumors and pathological centers. Ki67 antigen is a reliable indicator of tumor proliferative activity.Ki67 exists in the late G1, S, G2 and M phases of the cell cycle, but not in the G0 phase, and has a short half-life, which can be used to indicate the proliferative state of tumor cells. Generally, the higher the Ki67 positive rate, the more active the tumor proliferation, indicating poor differentiation, high malignancy and poor prognosis. The threshold of Ki67 positivity is different for different tumors. Generally speaking, 20-30% for breast cancer is the threshold of low expression and high expression, while 25% for cervical cancer and gastric cancer and 50% for thymoma are the threshold. Different hospital pathology centers have different values, it is recommended to compare the value of 20% with that of local hospitals to determine the level of 20%, if 20% is high expression, it means that the prognosis is poor; if 20% is low expression, the prognosis is good. Generally, the Ki67 positive rate is accompanied by (-) negative, (+) weak positive, (++) moderate positive, and (+++) strong positive. Generally, negative and weak positive are considered as low expression, while moderate and strong positive are considered as high expression. It is recommended that patients refer to the value determined by the local hospital, report other descriptions, other indicators, as well as the type and stage of the tumor to comprehensively determine the prognosis, and follow the doctor’s instructions to choose the appropriate treatment.