Embryonic stem cells are derived from the inner cell mass of the blastocyst and are unique in their pluripotent capacity and potential for self-renewal. Sox2 is one of a set of transcription factors that are crucial for the maintenance of pluripotency (1). Sox2, Oct-4, and Nanog cooperate in this network (1-3), and siRNA knockdown of either Sox2 or Oct-4 results in loss of pluripotency (4,5). Chromatin immunoprecipitation experiments have shown that Sox2 and Oct-4 bind to thousands of gene regulatory sites, highlighting the importance of these transcription factors in early embryonic development (6,7). It has recently been shown that Sox2 is amplified in lung and esophageal squamous cell tumors (8).