## 1 Introduction  
Breast cancer is the most common cancer among women [1], and it is a leading health concern among women due to its high mortality and morbidity rates [2]. Different imaging techniques for breast lesion characterization, alone or in combination, have been extensively evaluated with generally high sensitivity despite limited specificity values in the distinction between benign and malignant masses. Breast cancer is a heterogenous disease with various histologic subtypes, molecular profiles, behaviors, and responses to therapy. Among benign tumors, the most frequent lesions are fibroadenomas, while infiltratingductal carcinoma is the most common malignant lesion. After the histologic assessment and diagnosis of an invasive breast carcinoma, the use of biomarkers, multigene expression assays, and mutation profiling may be used in order to choose the proper treatment. Currently, mammography is widely recognized as the best technique in the early detection of breast cancer [3]. It allows a complete and repeatable breast evaluation with quality control and has maximal sensitivity values, especially in the initial phase of breast tumors. These features make mammography the best screening method in patients over 40 years of age. However, mammography has limitations. In a recent review, [PERSON] et al. [4] estimated the sensitivity for mammography for a one-year screening interval to be between 71% and 96%, with lower sensitivity observed in younger compared with older women. Factors known to affect mammographic sensitivity include breast density (being clearly better in fatty breasts), use of hormone replacement therapy, poor image quality, number of views, and the experience and skill of the interpreting physician. Greater experience in interpreting mammograms, independent double reading, and computer-aided detection have all been shown to improve mammographic sensitivity. Mammographic specificity was estimated between 94% and 97%. Most women with a false positive result on screening mammography usually undergo additional mammograms, ultrasound studies, or physical examinations, and the majority of these women are subsequently determined not to have breast cancer. This fact leads to an increase in healthcare costs and has a negative impact on patients' anxiety. Another problem of periodic mammography screening is overtreatment of benign lesions or the detection of less aggressive ductal carcinoma in situ (DCIS) in elderly patients who do not benefit from a reduction of mortality risk but may have a reduction of life quality from the treatment. Finally, another disadvantage of mammography is that it cannot be used as a periodic screening in young patients (under 35 years) and, in particular, in young patients with genetic mutations, such as BRCA-1 and BRCA-2 mutations, and in patients who underwent previous chest radiation therapy at a young age. All of these categories, which have a high risk for breast cancer but at the same time have increased radiosensitivity, should be screened only with ultrasound and magnetic resonance imaging, because neither uses ionizing radiation [5]. Ultrasound (US) was proven to be very useful in breast lesion differentiation, being a non-invasive, reproducible, and cost-effective technique, and became the first-line imaging in young women (especially before the age of 40) and the complementary method to mammography in older women with dense breast structure [6]. Ultrasound is also a useful tool in carrying out biopsy procedures. Its main limitations consist of being an operator-dependent technique and the substantial overlap of morphologic ultrasound features between benign and malignant lesions. With the introduction of the Breast Imaging Reporting and Data System (BI-RADS) for US [7], the criteria for describing and classifying breast nodules were standardized with good diagnostic performance.