CD133, also known as prominin-1, is a cholesterol-binding membrane glycoprotein encoded by the PROM1 gene. It is widely recognized as a marker for cancer stem cells and has multiple functions. Structurally, CD133 has a complex topology with five transmembrane domains and two large extracellular loops. Functionally, it plays a crucial role in the organization of plasma membrane protrusions such as microvilli and primary cilia. CD133 is involved in various signaling pathways, including PI3K-Akt, which promotes cell self-renewal, survival, and tumor formation. It also interacts with the Wnt/β-catenin pathway, influencing tissue development and regeneration. In addition, CD133 is associated with drug resistance in cancer cells through its involvement in pathways like PI3K/Akt and Hedgehog. Its expression is regulated by factors such as DNA methylation and signaling molecules like TGF-β.