Breast cancer is one of the most common malignant diseases among women worldwide. In China, the morbidity and mortality rate from breast cancer has increased significantly in recent years. Early diagnosis is crucial to ensure the best possible prognosis. Biopsy is an invasive technique and not recommended for screening. Palpation on the other hand, can detect superficial masses, but may miss small masses or masses deep beneath the skin. Mammography is the most frequently used screening method for detecting breast cancer; however, it has poor specificity, and its efficacy is limited in patients with dense breast tissue. Ultrasonography may overcome these limitations, and it has become the most important adjunct tool for breast cancer screening. It is also routinely used for guidance in breast mass biopsy.