Invasive lobular carcinoma of the breast: we diagnose it, but do we know what it is?

Invasive lobular carcinoma of the breast is the most common special type breast cancer. It has been defined using morphological features, has a characteristic immunophenotype associated with the loss of E-cadherin mediated intercellular adhesion, and the background of this immunohistochemistry and morphology is generally a biallelic genetic alteration of the CDH-1 gene coding E-cadherin. However, the morphology may often deviate from the classical, and immunohistochemistry may also deviate from the typical, and then the diagnosis of invasive lobular carcinoma becomes less straight forward. Eventually, the definitions of this histological type, although similar, are not identical and this may also give ground to occasional different interpretations. This review summarizes different approaches to invasive lobular carcinomas and the deviations from what is considered normal.