The proto-oncogene c-Kit (protein tyrosine kinase KIT or CD117), a transmembrane cytokine receptor, is phosphorylated and activated by binding to a KIT ligand called stem cell factor, which is a marker of SCSs in ovarian and endometrial cancers and osteosarcoma; however, the proposal that c-Kit is a marker of CSCs in cervical cancer is not yet proved. The gene discussed is KIT; the disease is osteosarcoma.