Lobular Breast Lesions

Invasive lobular carcinoma is the most common “special type” of breast carcinoma, accounting for 5–15% of invasive carcinomas. Lobular carcinomas have characteristic cytologic features and dyscohesive architecture, with one of the molecular hallmarks being loss of the cell adhesion molecule E-cadherin in atypical lobular hyperplasia, lobular carcinoma in situ, and invasive lobular carcinoma. In its classic form, invasive lobular carcinoma is usually estrogen receptor+/Her2- and shares other molecular alterations with luminal A/low-grade carcinomas. We present classic and variant forms of invasive and in situ lobular neoplasia, with clinical and radiologic correlation, and updated immunohistochemical and molecular features.