FAT4. a member of the atypical cadherin family, is a transmembrane protein encoded by the *FAT4* gene. It plays critical roles in cell adhesion, planar cell polarity (PCP), and tissue morphogenesis by regulating cell-cell interactions and cytoskeletal organization. Structurally, FAT4 contains multiple extracellular cadherin repeats, EGF-like domains, and laminin G motifs, enabling its participation in signaling pathways such as Hippo and Wnt. Dysregulation of FAT4 is linked to developmental disorders and cancers. For instance, mutations in *FAT4* are associated with Van Maldergem syndrome and Hennekam syndrome, characterized by lymphatic, neurological, and craniofacial abnormalities. In cancer, FAT4 often acts as a tumor suppressor; its loss or downregulation is observed in colorectal, breast, and gastric cancers, correlating with metastasis and poor prognosis. FAT4 antibodies are essential tools for studying its expression, localization, and function. They enable detection via techniques like Western blot, immunohistochemistry, and immunofluorescence, aiding research into FAT4's role in development, disease mechanisms, and potential therapeutic targets. Commercial FAT4 antibodies are typically validated for specificity against human or mouse isoforms, though cross-reactivity challenges may require careful experimental design.