CRK and breast cancer: Transient knockdown of CrkI/II and CrkL in combination resulted in a greater decrease in migration and invasion than single knockdown (CrkI/II or CrkL) alone (Additional file 5), supporting that Crk proteins have an additive role in promoting cell migration and invasion, and demonstrating a requirement to knock down all three Crk proteins within the 1833TR aggressive breast cancer cell line.