A hard lump in the breast that hurts when pressed may be related to mastitis, breast fibroadenoma, breast cancer and so on. 1. Mastitis: Mastitis is an inflammation of the breast tissue and is divided into two types: lactation and non-lactation. Breastfeeding mastitis will show redness, swelling, heat and pain in the breast, while non-breastfeeding mastitis will have lumps and will be obviously painful. So when the breast is hard and painful to press, you can consider that it is caused by mastitis. 2. Mammary fibroadenoma: Mammary fibroadenoma is a common benign tumor of the breast, which may appear as a movable breast lump, varying in size and may be accompanied by pain. 3. Breast Cancer: Breast cancer is a malignant tumor formed by uncontrolled proliferation of breast epithelial tissues under the action of various carcinogenic factors. Breast cancer will appear breast lumps, nipple and areola changes, etc. Breast lumps may be painful when pressed. In addition, breast hyperplasia, breast trauma, breast cysts and other diseases may also appear similar manifestations, it is recommended that patients with hard breast lumps that are painful to press go to the hospital to do the relevant examinations, to clarify the specific causes of the disease, and then receive targeted treatment from the doctor.