ROR2 and breast cancer: Next, we aimed to unravel the molecular events that underlie the unfavorable prognostic role of ROR2. Since ROR1 and ROR2 are known to interact and compensate for each other, we choose to limit potential cross-reactivity by stably overexpressing ROR2 in the ROR-negative [9] human breast cancer cell lines MCF-7, SK-BR-3 and BT-474 (Fig. 1d).