ROR1 and B-cell chronic lymphocytic leukemia: In this study, we found that the pre-treatment CLL cells of seven patients who subsequently failed to clear MRD each expressed levels of ROR1 comparable to those in the top 25th percentile of a large cohort of patients with CLL, indicating a significant association between the subsequent failure to clear MRD with high-level expression of ROR1 prior to therapy (p = (0.25)7, or 0.00006).