A large hard lump inside the breast is considered to be caused by the following conditions: First, it may be suffering from breast hyperplasia, which is a relatively common breast disease in adult women, mostly related to the patient’s endocrine disorders, there will be hard lumps inside the breast, abnormal breast overflow and breast pain and other symptoms, and there is a relationship with the menstrual cycle, the hard lump in the breast before the onset of menstruation will be harder, breast pain The symptoms will gradually ease after the onset of menstruation. Secondly, it may be mastitis, especially during breastfeeding, which is most likely to occur in women, mostly due to the accumulation of milk, with hard lumps and painful redness; thirdly, it may be breast cancer, especially in the late stage of breast cancer, with hard lumps and painfulness in the breast. Fourth, it may also be caused by breast fibroids and other diseases, and it is recommended to go to the hospital for corresponding examination and treatment in time.