Breast ultrasound category 4a is more serious if caused by breast cancer, and mostly less serious if caused by benign breast disease. The BI-RADS (Breast Imaging Reporting and Data System) classification is a malignancy risk assessment of breast nodules based on the results of ultrasound, mammogram and other breast imaging tests, where category 4a is defined as low suspicion of malignancy, with a 2-10% risk of being caused by malignant tumors such as breast cancer. If category 4a nodules are caused by benign non-neoplastic diseases such as breast cysts, breast hyperplasia, or benign tumors such as fibromas and intraductal papillomas, they are not serious, and can be significantly improved or cured by symptomatic treatment as well as surgical excision. If category 4a nodules are caused by malignant tumors such as breast cancer, they are more serious. Early stage breast cancer can be clinically cured through radical surgery, chemotherapy, endocrine therapy and other comprehensive treatments, with a good prognosis; however, more advanced breast cancer will affect survival and even endanger life. Patients are advised to consult a specialist and undergo tests such as MRI and puncture biopsy when necessary.