Malignant tumors of the breast are caused by genetic mutations in normal tissues. Malignant tumors originating from the epithelial tissue of the breast are called breast cancer; malignant tumors originating from the non-epithelial tissue of the breast are breast sarcomas. Once suffering from tumor, it makes people very worried and panic, therefore, below I will share with you how to identify whether breast tumor is benign or malignant. I. Shape, density and edge Benign masses are mostly oval and round with increased density shadow, smooth and sharp border, usually single, and fibroadenoma may be multiple. There are also some benign tumors such as encapsulated hematoma, mismatched tumor and lipid cyst with higher density. However, a few malignant tumors are also oval in shape with smooth and sharp margins, such as simple carcinoma or medullary carcinoma, which are easily misdiagnosed as benign lesions. Malignant tumors are often lobulated, stellate or burr-like, which is due to infiltrative growth in the surrounding tissues between the carcinomas. In addition, the tumor shadow of benign lesions on X-ray often conforms to the size of the tumor on palpation, while breast cancer tumors have the characteristic of being large on palpation but small on image, and the lump shadow shown on X-ray is often about 1/2 of the size on palpation. Therefore, it is especially important for radiologists to perform clinical examination while observing the X-ray film. Benign calcifications are mostly distributed in the interstitium and are sparsely scattered, uneven and variable in shape, with >5 calcifications/cm2 within the mass. In malignant tumors, peri-calcifications are distributed in the parenchyma of the ducts and lobules of the breast, with uneven density and varying size, and the number of micro-calcifications is >20/cm2, with the morphology of small rods, small dots and mud-like, mostly outside the tumor boundary. There are also some patients with microcalcifications on X-ray, but the mass cannot be palpated clinically, they should be reviewed regularly and directional puncture should be done if necessary, which can improve the diagnosis rate of early cancer and microscopic cancer. Changes of surrounding blood vessels and surrounding tissues Benign tumors do not have thickened surrounding blood vessels, and the blood vessels are generally under pressure. The mass is compressed and pushed to the surrounding tissues, and the local glandular structure is clear. In malignant tumors, thickened draining vessels or disorganized vessels can be seen around the tumor. Under normal circumstances, the left breast vein is slightly thicker than the right breast vein. It is believed that if the ratio exceeds 1:14, the presence of breast cancer should be considered as a possibility and should be followed up. Due to the fibroproliferative response of human tissues to malignant tumors, the interface between fat and normal breast parenchyma is distorted, so the tissues around malignant tumors are blurred, deformed, lose their normal shape, and cross normal tissues. In dense mammary glands, the mass shadow is obscured by the gland. The only indication of malignancy may be local structural disorder, at this time, ultrasound exploration or multiple biopsies are feasible to exclude the possibility of cancer. In benign tumors, the nipple overflow is mostly yellow or milky white, and the ductogram shows a round or round-like filling defect with smooth surface or a mid-duct, and the duct section is “cup-shaped”, the duct dilatation is not obvious, and the duct curvature is soft. In malignant tumors, the papillary discharge is mostly bloody. The ductography shows dilated ducts with irregular and stiff walls and irregular, cauliflower-shaped filling defects in the lumen. V. Nipple indentation and skin thickening This sign is mostly seen in malignant tumors, mainly due to cancer cell infiltration, congestion and lymphedema in the ducts, glandular structures and skin lymphatic vessels. However, nipple depression and skin thickening can also be seen in acute mastitis and ductitis, which should be closely related to the clinical history. In conclusion, as a radiologist, we should not only recognize the characteristic X-ray manifestations of benign and malignant breast tumors, but also carefully observe the subtle indirect signs and symptoms. For women with family history, prevalent age group and breast with bundle and mixed type, we should follow up and observe regularly. Only in this way, the diagnosis of breast cancer can be greatly improved.