ROR1 and breast cancer: Previous studies demonstrated that ROR1+ breast-cancer cells had a greater capacity to metastasize than breast-cancer cells silenced for ROR1.9 Consistent with these findings, we found that the numbers of metastatic foci detected in the lungs of mice 1 (Fig. 4a, b) or 3 weeks (Fig. 4c, d) following intravenous injection of MCF7–ROR1 cells were significantly greater than those detected in the lungs of mice injected with equal numbers of MCF7 cells.