Evolving concepts in breast lobular neoplasia and invasive lobular carcinoma, and their impact on imaging methods.

Invasive lobular carcinoma (ILC) and lobular neoplasia (LN) are two distinct conditions that still pose challenges regarding to their classification, diagnosis and management. Although they share similar cellular characteristics, such as discohesive neoplastic cells and absence of e-cadherin staining, they represent completely different conditions. LN encompasses atypical lobular hyperplasia (ALH) and lobular carcinoma in situ (LCIS), which are currently considered risk factors and non-obligatory precursors of breast neoplasia. These lesions are diagnosed as incidental findings in percutaneous biopsies or appear as non-specific clusters of punctate calcifications in mammograms. ILC is the second most common breast malignancy and has typical histological features, such as infiltrative growth and low desmoplasia. These histological features are reflected in imaging findings and constitute the reasons for typical subtle mammographic features of ILC, as architectural distortion or focal asymmetries. Ultrasonography (US) may detect almost 75 % of the ILCs missed by mammography and represents the modality of choice for guiding biopsies. Magnetic resonance imaging (MRI) exhibits a high sensitivity for the diagnosis of ILC and for detecting synchronous lesions. Teaching Points • LN includes ALH and LCIS, risk factors and non-obligatory precursors of breast cancer.• Absence of e-cadherin staining is crucial for differentiation among ductal and lobular lesions. • ILC has typical histological features, such as infiltrative growth and low desmoplasia. • Mammographic features of ILC are often subtle and reflect the histological features. • MRI exhibits a high sensitivity for the diagnosis of ILC and for detecting synchronous lesions.