[Invasive lobular carcinoma: Clinicopathologic and biological insights]

Invasive lobular carcinoma (ILC), the second most common histologic subtype of breast cancer, is a clinicopathologic entity distinct from invasive carcinoma of no special type. It is defined by loss of E-cadherin (inactivation of CDH1 gene), which underlies the characteristic discohesive tumor cells, and is associated with ill-defined growth pattern, frequent multifocality and bilaterality, and a distinctive pattern of metastases (peritoneum, meninges, ovaries, gastrointestinal tract). Recent work has delineated several lobular-specific biological features, supporting the development of ILC-directed targeted therapies. In this context, improving diagnostic reproducibility (still suboptimal) remains a priority for pathologists. In 2024, the European Lobular Breast Cancer Consortium called for standardization of diagnostic practice, including codified use of immunohistochemistry. This review synthesizes the current diagnostic, biological, and therapeutic landscape of ILC amid renewed interest within the medical and scientific community.