A humanized monoclonal antibody against the extracellular domain of the human receptor tyrosine kinase-like orphan receptor 1 (ROR1), with potential antineoplastic activity. Upon administration, cirmtuzumab binds to ROR1 and blocks ROR1-mediated signaling. This prevents tumor cell proliferation in cancer cells overexpressing ROR1. ROR1, also known as neurotrophic tyrosine kinase, receptor-related 1 (NTRKR1), is normally expressed during embryogenesis. It is overexpressed in certain leukemias and solid tumors, but minimally expressed in healthy cells.