Breast nodule category 4A refers to a low malignancy potential with a malignancy rate of 2-10%; an aspect ratio >1 is a sign that the nodule is suspicious for malignancy. The BI-RADS (Breast Imaging Reporting and Data System) classification of breast nodules is an assessment of the risk of malignancy of a nodule from ultrasonographic findings. One category, 4A, means that there is a low likelihood of malignancy, with a 2-10% risk of a malignant nodule such as breast cancer, but the majority are still benign nodules such as fibroids. A breast nodule with an aspect ratio greater than one indicates that morphologically the nodule is more likely to be malignant. The measurement is based on the ratio between the transverse diameter of the nodule parallel to the skin and the longitudinal diameter of the nodule perpendicular to the skin under the ultrasound scanner. Based on the ratio, the benign or malignant status of the nodule is inferred. If the aspect ratio is less than one, the tumor is usually benign, and if the aspect ratio is greater than one, the tumor is more likely to be malignant. To determine the nature of the tumor, the results of other tests, such as mammography, puncture biopsy or pathology after surgical excision, are needed. The aspect ratio of the breast nodule is to provide some reference value for the syndromic condition of the breast tumor, and it does not mean that an aspect ratio greater than one is necessarily malignant. Histologic examination is generally recommended for patients with category 4A breast nodules to further clarify the nature of the nodules. Patients are advised to seek timely medical attention and follow the doctor’s instructions for examination and treatment.