CD133, also known as prominin-1, is a pentaspan transmembrane glycoprotein encoded by the PROM1 gene. It is widely recognized as a biomarker for the isolation and identification of stem cells and cancer stem cells (CSCs) in various tissues and cancers. This 97-kDa protein features five transmembrane domains, with its N-terminus extending into the extracellular space and the C-terminus residing intracellularly. CD133 is predominantly expressed in cellular protrusions and has been associated with tumorigenesis, metastasis, chemotherapy resistance, and poor prognosis in several cancers, including colorectal, liver, and breast cancer. Additionally, CD133+ cells have demonstrated angiogenic potential and may play a role in tumor vascularization. Recent studies also suggest that CD133 could serve as a predictive marker for anti-angiogenic therapies, such as bevacizumab treatment in metastatic colorectal cancer.