If the breast lump is larger than 3cm, it needs attention. However, there is not much relationship between the size of breast lump and the benign or malignant nature of the tumor, and the determination of the benign or malignant nature of the tumor is mainly based on pathological examination such as puncture. Breast malignant tumor can be divided into invasive carcinoma and non-invasive carcinoma. When non-invasive carcinoma grows in situ without breaking through the basement membrane, it can continue to increase in size, and clinically manifested as painless breast lump, irregular edge, unclear border and poor mobility, then we should raise alert, which may be malignant tumor. In early stage, invasive carcinoma can break through basement membrane, invade surrounding blood vessels and lymphatic channels for metastasis, and multiple lumps can appear in breast, but the volume is small, and there are no special symptoms in early stage, but in late stage, it can cause breast pain, nipple milk overflow, and palpable enlarged lymph nodes, etc. Therefore, it is not possible to diagnose based on the size of lump. Therefore, the judgment of benign or malignant lesions cannot be made according to the size of the lumps, but needs to be based on breast ultrasound, CT, and biopsy and puncture if necessary. It is recommended that patients go to regular hospitals as soon as possible to improve the examination, do not blindly self-governance, in order to avoid misunderstanding the condition.