CXCR4 and neoplasm: Established CSC markers are expressed in various types of solid tumors, including neuroblastoma, such as chemokine receptor CXCR4, associated with migration, metastasis and tumor growth [28,29,30,31,32]; pluripotency-driving transcription factor NANOG, correlating with metastasis and poor prognosis [28,33]; as well as self-renewal factor BMI1, involved in tumorigenesis and chemoresistance [27,29].