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. This evidence concerns the gene ROR1 and breast carcinoma.