BCAR1 (BCAR1 scaffold protein, Cas family member) is an adaptor protein that functions as a central coordinator for tyrosine kinase-based signaling pathways related to cell adhesion, migration, and survival 1. The protein lacks enzymatic or transcriptional activity but contains modular binding motifs that enable formation of multi-protein signaling complexes, resulting in pleiotropic effects on cell motility, cytoskeleton remodeling, invasion, and proliferation 1. BCAR1 mediates these functions through interactions with multiple signaling pathways, including SRC kinase signaling to promote E-cadherin degradation and removal from cell membranes 2, and ERK signaling to enhance cell migration and invasion 3. The protein is significantly associated with cancer progression and therapeutic resistance. BCAR1 overexpression correlates with antiestrogen resistance in breast cancer, particularly tamoxifen resistance in estrogen receptor-positive tumors 4. High BCAR1 expression predicts poor prognosis in breast cancer patients and is associated with increased malignancy across various cancer types 51. Additionally, BCAR1 variants show associations with metabolic disorders, including type 2 diabetes mellitus in Chinese populations 6, suggesting broader roles in cellular homeostasis beyond cancer.