The Role of Receptor Tyrosine Kinase-like Orphan Receptor 1 (ROR1) in Cancer Stem Cell Signaling.

Receptor tyrosine kinase-like orphan receptor 1 (ROR1) is a key regulator of cancer stem cell (CSC) biology and signaling. In CSCs, ROR1 acts as a receptor or co-receptor, interacting with non-canonical WNT ligands, and forming complexes with proteins like CD19 and HER2, to activate diverse downstream signaling pathways. ROR1 signaling in CSCs promotes proliferation, maintains stemness, and enhances migration, invasion, and the epithelial-to-mesenchymal transition (EMT). While minimally expressed after embryogenesis, ROR1 is aberrantly upregulated in numerous cancers, including ovarian, breast, pancreatic, and hematologic malignancies. ROR1 overexpression drives tumor progression, resistance to chemotherapies, disease recurrence, and ultimately metastasis. This expression pattern positions ROR1 as a promising target for CSC-specific therapies. High ROR1 expression is consistently linked to aggressive disease and poor patient outcomes. Here, we review ROR1's role in CSCs and highlight the complex signaling that is observed in the CSC population. Further, we evaluate the gaps in the current understanding of ROR1 signaling in CSCs and describe how ROR1 regulates the associated signaling pathways. Finally, we provide an up-to-date summary of the promising therapeutic strategies targeting ROR1 that overcome conventional cancer treatment limitations. This review highlights the role of ROR1 as a critical, functional driver of CSCs and adverse patient outcomes across various malignancies.