If you have a large hard lump in your breast, it may be caused by the following reasons: 1. breast accumulation: If you are pregnant or postpartum, it is often the disease, do not worry too much, you can actively promote lactation, if necessary, you can also apply hot compresses to improve the symptoms of discomfort, and sometimes you need to use a breast pump to suck the breast. 2. benign breast diseases: such as fibroadenoma of the breast, you need to go to the hospital to check the ultrasound or mammogram photos, etc. If the disease is clear, it can be observed regularly. 3. Malignant breast tumor: Breast cancer is caused by mammography and mammogram, so you need to check the ultrasound and mammography as soon as possible. If it is clear that the tumor is malignant, radical resection of the tumor is needed, together with lymph node dissection, and other treatments are needed later.