Breast cancer anti-estrogen resistance protein 1 is a protein that in humans is encoded by the BCAR1 gene. BCAR1 is a ubiquitously expressed adaptor molecule originally identified as the major substrate of v-Src and v-Crk . p130Cas/BCAR1 belongs to the Cas family of adaptor proteins and can act as a docking protein for several signalling partners. Due to its ability to associate with multiple signaling partners, p130Cas/BCAR1 contributes to the regulation to a variety of signaling pathways leading to cell adhesion, migration, invasion, apoptosis, hypoxia and mechanical forces. p130Cas/BCAR1 plays a role in cell transformation and cancer progression and alterations of p130Cas/BCAR1 expression and the resulting activation of selective signalling are determinants for the occurrence of different types of human tumors.