The most striking upregulation, however, is the expression of Receptor Tyrosine Kinase-Like Orphan Receptor-1 (ROR1)—a membrane receptor for WNT-5A— that is uniquely upregulated in CLL cells [29,64,65] and in most other mature-B cell lymphomas [66], while its expression in normal B cell or leukocyte populations is very limited. Here, ROR1 is linked to B-cell chronic lymphocytic leukemia.