A solid breast mass is a mass with a substantial structure within it, and BI-RADS category 4C refers to a high malignant potential, with a malignancy rate of 50-95%. Breast lumps can be classified as solid, cystic, cystic-solid, etc. Solid is the concept opposite to cystic, solid lump means that the inside of the lump is a substantial structure such as cells and fibrous tissues, and cystic lump means that the inside of the lump is a cystic fluid such as sloughed off milk, necrotic liquefied material, and bloody fluid. A solid breast lump may be the result of benign diseases such as hyperplastic breast lump, breast fibroma, intraductal papilloma, or malignant tumors such as breast cancer. The BI-RADS (Breast Imaging Reporting and Data System) classification is an assessment of the risk of malignancy of a breast nodule based on the results of imaging tests such as ultrasound. category 4C means that the breast nodule is highly malignant with a 50-95% risk of malignancy, i.e., there is a 50-95% likelihood that a category 4C solid breast mass is caused by breast cancer. Generally, category 4C solid breast lumps need to undergo puncture or excisional biopsy to further define the benign or malignant nature of the lumps. It is recommended to consult a specialist and follow the doctor’s instructions for further examination and treatment.