A lump on the breast may be caused by breast sebaceous cyst, breast hyperplasia, breast fibroadenoma, breast cancer and other reasons, you should go to the hospital in time for examination to clarify the cause of the disease. 1. Breast sebaceous cyst: It is due to the blockage of sebaceous glands, poor drainage, so that a large amount of sebum is stored in the glands, when the symptoms occur in the skin of the breast for the breast sebaceous cyst, which can lead to the symptom of a small lump on the breast. 2. Mammary hyperplasia: when the endocrine function in the body is disturbed, the breast tissue appears to be hyperplasia or degenerative disease, which can lead to the symptom of a lump on the breast, and there will be pain in the breast, and some of the patients will have nipple discharge and other symptoms. 3. Breast fibroadenoma: the most common benign breast tumor, mostly occurring in young and middle-aged women, manifested as round or oval breast lumps, smooth surface, good mobility, and can be cured after surgical excision. 4. Breast cancer: the most common malignant tumor of the breast in women, the age of onset is gradually younger, mostly using surgery as the main comprehensive treatment, advocating “early detection, early treatment”. There are many reasons why there is a lump on the breast, and when symptoms occur, you should go to the hospital in time for relevant examinations to clarify the cause of the disease and carry out targeted treatment as soon as possible, so as to avoid the impact on the body.