ROR1 (neurotrophic tyrosine kinase, receptor-related 1, NTRKR1) is a receptor tyrosine kinase that regulates the growth of neurites in the central nervous system. ROR1 controls synapse formation in hippocampal neurons in complex with ROR2, and the degree of ROR1 expression dictates the number and length of axonal branches extended by neurons. ROR1 has also been found to be vital for the development of hearing and the inner ear in humans and mice. In cancer, ROR1 promotes invasion in ovarian carcinoma and is a potential target of antibody inhibition therapies, particularly since ROR1 has generally low (but not absent) expression in adult tissue. In immunohistochemistry, ROR1 has highest positive membranous staining in parathyroid tissue, pancreatic islets, and some areas of the duodenum, esophagus and stomach. References: Proceedings of the National Academy of Sciences of the United States of America. 111 (48): 17266–71, PMID: 25411317; J Cell Sci. 2005 Jan 15;118(Pt 2):433-46, PMID: 15654020; Protein Cell. 2014 Jul; 5(7): 496–502, PMID: 24752542; Neuroscience. 2010 Feb 17;165(4):1261-74, PMID: 19958813; PNAS May 24, 2016 113 (21) 5993-5998, DOI: 10.1073/pnas.1522512113; Clin Cancer Res. 2017 Jun 15;23(12):3061-3071