SOX2 and cancer: OCT4, SOX2, NANOG, KLF4, and c-MYC act cooperatively to promote pluripotency (37), and consequently, some or all of these markers have been used to identify CSC subpopulations in many cancer types, including HNcSCC (19), OCSCC affecting different subsites (38–40), glioblastoma (41), renal clear cell carcinoma (17), primary (18), and metastatic (42) colon adenocarcinoma, and metastatic malignant melanoma (43, 44).