There are many reasons for finding a significant hypoechoic nodule in the left breast. The first is a malignant nodule that occurs in the breast and has a clear family tendency to run in families. If there are high-risk factors, the nodule should be found promptly for examination, including mammography of the breast, or MRI of the breast. The cause of malignant breast disease is also related to changes in hormone levels in the body, caused by an imbalance in the ratio of estrogen to progesterone. The second is cystic hypoechoic nodules in the breast, which are mainly caused by dilated milk ducts and are associated with mastopexy. Excessive hyperplasia or uncoordinated hyperplasia of the breast gland can also result in nodules, and even localized cystic changes and dilatation of the milk ducts, which can manifest as low-density lesions, with regular, smooth margins noted on examination.