The pathohistological grading of mucinous breast cancer is divided into 3 grades: G1, G2 and G3. G1 belongs to low grade, G2 belongs to middle grade and G3 belongs to high grade, the higher the grade, the higher the malignant degree of mucinous breast cancer, and the more prone to spread and metastasis of tumor cells. For the same clinical stage of breast cancer, if the pathological histology is G3, its prognosis is worse than that of G1 and G2, even through the comprehensive anti-tumor treatment such as surgery, radiotherapy, chemotherapy, endocrine therapy, targeted therapy, etc., but the 5-year survival rate of G3 is lower than that of G1 and G21. However, if the tumor is detected early and all the cancer cells in the body can be killed through treatment, G3 may also be cured.