Receptor-tyrosine-kinase-like orphan receptor 1 (ROR1) is a tumor-associated, surface protein predominantly expressed during embryogenesis, where it is involved in organ morphogenesis, nervous system development, and neural progenitor cell maintenance and survival. Virtually absent from normal pediatric and adult tissues, with the exception of low-level expression in a subset of immature B-cell precursors known as hematogones and adipocytes, ROR1 is notably overexpressed, and considered a survival factor, in a number of B lymphoid and epithelial malignancies: most notably, but not exclusively, including chronic lymphocytic leukemia (CLL), mantle cell lymphoma (MCL), acute lymphoblastic leukemia (ALL), marginal zone lymphoma, lung adenocarcinoma. First identified during PCR-based cloning of a human neuroblastoma cell line in search of tyrosine kinases similar to tropomyosin-receptor-kinase (Trk) neurotropic receptors, ROR1, along with the related receptor tyrosine kinase (RTK) ROR2, was catalogued as an “orphan” receptor due to the fact its related ligand remained elusive. Wnt-5a has since been suggested as a candidate ligand for ROR1, and ROR1 has been implicated to function as a pseudokinase, promoting proliferation and resistance to apoptosis in cancer cells through interaction with Wnt-5a, and TCL1-co-activation of AKT. ROR1 is expressed as a glycoprotein containing extracellular immunoglobulin (Ig)-like, Frizzled, and Kringle domains, as well as an intracellular region containing a tyrosine kinase domain. PeproTech’s Recombinant Human ROR1 is a glycoprotein containing 377 amino acid residues, and has a calculated molecular weight of approximately 42.4 kDa. As a result of glycosylation, Recombinant Human ROR1 migrates with an apparent molecular mass of approximately 55-65 kDa by SDS-PAGE gel, under reducing and non-reducing conditions.