ROR1 and breast cancer: Cortactin contains a SH3 domain, which can bind to –P–X–X–P– sites that typically are found within the PRDs of other proteins, including ROR1.1,28–30 Previously we described that PRD or proline at 841 of ROR1 was required for ROR1/cortactin association and phosphorylation of cortactin in CLL cells.15 Here, we examined whether the ROR1–PRD was necessary for ROR1 to complex with cortactin in breast-cancer cells.