Benign tumors, such as fibroadenoma, and malignant tumors, such as intraductal carcinoma in situ or invasive carcinoma, can occur in the breast. Both benign breast tumors and malignant breast tumors are breast nodules under ultrasound. In benign breast tumors, the internal echogenicity of the nodule is uniform, the boundary of the nodule is clear, the nodule is mobile, and the nodule has no blood flow signal. What does an ultrasound of a malignant breast tumor look like? The nodule is inactive, the boundary of the nodule is blurred, and the echogenicity inside the nodule is mixed echogenicity, which is not uniform. The most critical thing is that the blood flow signal inside the nodule is extremely rich. Therefore, the most critical difference between benign and malignant tumors from ultrasound is the internal blood flow signal. If the internal blood flow signal is extremely rich, the possibility of malignancy should be considered.