Breast cancer (BC) is classified by extension into unifocal and multiple synchronous foci, which include multifocal, multicentric, and diffuse types (such as inflammatory BC, which may affect one or more lobes of the breast). Intramammary metastases are extremely rare at the time of imaging diagnosis and are not the subject of this study. Radiological-imaging diagnosis and postoperative characterization of multicentric and multifocal tumors depend on localization in arbitrarily established quadrants, which are illogical for mammography that considerably deforms the breast by compression in two non-orthogonal views. Moreover, the orthogonal scans and the same quadrants were borrowed by classical Ultrasonography and Magnetic Resonance Imaging, despite the specific anatomical breast architecture represented by 15-25 glandular lobes with radial arrangement around the nipple.

We aim to present and illustrate aspects of multiple BC using the concept of Full Breast Ultrasonography, which allows anatomical localization and assessment of extension based on radial and antiradial scanning around the nipple; an intralobular ductal connection of lesions is considered for multifocal, usually monoclonal cancers, with the assumption that a lobe may extend into two adjacent breast quadrants. Localization in different mammary lobes is an argument for multicentric, pathologically proven multiclonal cancers, regardless of belonging to mammary quadrants. The prevalence of multiple BC in our series was around 40%, higher than in MRI reports. Normal and abnormal lobar architecture is illustrated and sustained by the “Sick lobe theory” and the “gross section” in pathology promoted by T. Tot. The differential diagnosis of multifocal from multicentric cancers allows a personalized oncological treatment, a better choice of conservative or radical surgical approach, minimization of postoperative local recurrences, and improved life expectancy.

In conclusion, instead of delimiting the quadrants established by the BI-RADS system, the lobar criterion is recommended for assessing the extension and discriminating between unifocal, multifocal, and multicentric BC.