Mucinous adenocarcinoma of the breast, a rare type of special invasive breast cancer, accounts for 1%-3% of all breast cancers. Clinical characteristics 1. older age, mostly occurring in postmenopausal women over 50 years old; 2. staging foci; 3. low rate of lymph node metastasis; 4. ER and PR positive, low rate of HER2 positive. Pathological staging criteria Pathological features are: cancer tissue contains a large amount of mucus, and cancer cells often float in the mucus. Mucinous carcinoma of breast is classified into simple type and mixed type according to whether it contains infiltrative cancer components. In simple mucinous carcinoma, mucus accounts for more than 50% of the tumor volume. Mixed type mucinous carcinoma contains infiltrative carcinoma areas that lack extracellular mucus. Imaging performance B ultrasound: nearly half of them show swelling growth, rich in mucus, irregular morphology, unclear boundary and uneven internal echogenicity. Mammography X-ray: Most of them show clear boundaries and light density of the mass, and some of them nearly resemble benign tumor performance. Treatment Treatment according to TNM stage, low invasiveness, breast conservation in some patients, biopsy of anterior lymph nodes, axillary clearance can be avoided and quality of life can be improved. If the disease is very advanced, postoperative radiotherapy is still necessary. positive ER/PR suggests feasible endocrine therapy with good prognosis. evaluation of HER2 is divided into four grades of 0, 1+, ++, ++++, ++ or ++++ suggests positive, further genetic FISH genetic testing. Prognosis It is a low-grade malignant tumor with a good prognosis. The survival rates of 5, 10, 15 and 20 years were reported to be 94%, 89%, 85% and 81%, respectively, which are significantly better than that of common invasive ductal carcinoma of the breast.