The CLL cells that express high levels of ROR1 (ROR1Hi CLL) have differences in gene expression from CLL cells that express low-to-negligible levels of ROR1 (ROR1Lo CLL); such gene expression differences also are observed between ROR1-expressing leukemia cells that develop in Eμ-ROR1/TCL1-trangenic mice versus the ROR1-negative leukemia cells of Eμ-TCL1 transgenic mice [20, 24]. The gene discussed is ROR1; the disease is B-cell chronic lymphocytic leukemia.