Sox9 is a transcription factor with an HMG-box DNA binding domain that has homology to the HMG domain of the mammalian testis-determining factor, SRY. Sox9 regulates several important processes during embryonic development including chondrogenesis, during which it contributes to skeletal formation and digit specification. Sox9 also coordinates with steroidogenic factor-1 to direct Sertoli cell-specific expression of anti-Mullerian hormone during embryogenesis, thereby contributing to male sex determination. In addition, Sox9 is reportedly involved in the maintenance of adult stem cell populations, including multipotent neural stem cells, hair follicle stem cells, and mammary stem cells. Recent interest has focused on the role of Sox9 in tumor biology. For example, research studies have shown that Sox9 expression in lung adenocarcinoma induces a mesenchymal phenotype in tumor cells. Other research studies have shown that YAP1 induced upregulation of Sox9 confers cancer stem cell like properties on esophageal cancer cells. Moreover, Sox9 expression has been linked with several other tumor types including ovarian, prostate, and pancreatic malignancies.