A hard lump on one side of the breast is not normal and is considered to be a pathological change, which also requires timely examination by color ultrasound or B-mode ultrasound of the breast. Hard lumps in the breast can be caused by a variety of diseases, the most common of which are tumors, specifically benign and malignant. Malignant tumors, including breast cancer and breast sarcomas, as well as some lymphomas, are very rare, while benign diseases are commonly known as fibroadenomas. These diseases are characterized by hard lumps in the breast gland and even painful symptoms. Some patients may have nipple discharge, nipple invagination or enlarged axillary lymph nodes. The most effective treatment for breast tumors is surgery, especially for malignant tumors, and radical resection is required, as the cause of breast tumors is affected by changes in hormone levels in the body.