Breast cancer is only classified as low grade, intermediate grade and high grade when it is in situ. If the cancer is already invasive, it should be graded into grade I, II and III according to cytology. Low-grade ductal carcinoma in situ is the mildest of the relative carcinomas in situ, that is, the least heterogeneous cells, and it is closer to benign, so to speak, but it is still a carcinoma in situ. As the grade increases, the cellular anisotropy becomes more severe, but there may be no particular essential difference in treatment because it is all in situ cancer. If it refers to invasive ductal carcinoma, if it is between grade I-III, which is relatively low grade, it means that the heterogeneity of the cells is lower and should have a better prognosis.