Biological diversity of ILC is reflected in molecular subtypes defined on the basis of standard biomarkers analyzed via immunohistochemistry: estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor-2 receptor (HER2) as well as the estimation of tumor proliferation index Ki67 that allows risk stratification and implementation of personalized therapies. This evidence concerns the gene ESR1 and neoplasm.